As December approaches, major stock indices are poised for a routine reshuffle of their constituents. The CSI 300 Index, a benchmark often regarded as the barometer of China’s A-share market, is drawing significant investor attention with each adjustment. According to forecasts from leading securities firms, this round of adjustments is expected to involve 17 stocks.

Regular index reviews generally follow a three-stage process. Stock indices are reviewed semiannually, typically in May and November. The reference period for these reviews generally ends about one and a half months before the adjustment takes effect. The finalized adjustment list is announced two to three weeks prior to the implementation date, when the new constituents officially take effect.

Both the CSI and SSE index series follow the same review timelines and reference periods. For the mid-year review in late May, the reference period spans from May 1 of the previous year to April 30 of the current year, with the adjustment taking effect on the trading day following the second Friday of June. Similarly, for the year-end review in late November, the reference period covers November 1 of the previous year to October 31 of the current year, and the adjustment is implemented on the trading day after the second Friday of December.

According to rules set by the China Securities Index Company, stocks must meet several criteria to be included in the sample space, such as a minimum listing period (at least one year for Sci-Tech Innovation Board and ChiNext stocks, and one quarter for others), and exclusion of ST/*ST stocks. Additional requirements include average daily turnover ranking in the top 50% and average total market capitalization within the top 300 for the CSI 300 or ranks 301–800 for the CSI 500. A “buffer rule” also applies—for instance, the top 240 new candidates for the CSI 300 are prioritized for inclusion, while existing constituents within the top 360 are retained to minimize frequent turnover. For the upcoming December 2025 adjustment, the reference period runs from November 1, 2024, to October 31, 2025. Stocks showing notable market cap growth and meeting liquidity standards during this period are more likely to be included.

In recent years, as investor acceptance of index-based investing has grown, the scale of index funds has continued to expand. From the first quarter of 2010 to the third quarter of 2025, the scale of equity ETF assets has shown a consistent upward trend. By the end of the third quarter of 2025, the total scale of equity ETFs reached ¥4.11 trillion. Over the same period, the growth of conventional equity index funds (excluding ETFs) was relatively slower, influenced by factors such as the phase-out of structured funds, though a slight rebound was observed in Q3 2025.

As of October 31, 2025, the total assets under management (AUM) of passive and enhanced index funds tracking the CSI 300 stood at ¥1,350.9 billion. For the CSI 500, the corresponding AUM reached ¥229.5 billion, while the Sci-Tech Innovation Board 50 Index attracted ¥183.2 billion in tracking funds.

Wei Jianrong, head of the Financial Engineering team at Kaiyuan Securities, noted, “Since 2020, across all adjustment cycles, stocks added to or removed from the CSI 300 and CSI 500 indices have shown significant cumulative excess returns relative to the benchmark in the 60 trading days before and after the adjustment. The market tends to price in the impact of index changes ahead of time. Investors often trade in anticipation of the reshuffle based on predictable rules, leading to opposite directional effects: stocks to be added tend to rise before inclusion, while those to be removed often decline ahead of the official adjustment.”

As a key barometer of the A-share market, the CSI 300 is expected to see 17 changes this round, with new inclusions concentrated in sectors such as power equipment, electronics, and transportation. The 17 potential new constituents are: Huadian New Energy, Shenghong Technology, Shanghai Electric, Guangqi Technology, Ningbo Port, Rockchip, Huagong Tech, Dongshan Precision, Enlight Media, Guidepoint, Anker Innovations, Guolian Minsheng, Tuojing Technology, Zhongtian Technology, San’an Optoelectronics, Hainan Airlines, and Sinoway.

By Liu Yang