T+1 trading mechanism causes negative overnight return

The T+1 trading mechanism is unique in the Chinese stock market, thus providing a natural experimental field to study the trading mechanism and price behaviors. This paper proposes and proves that T+1 trading mechanism causes negative overnight return, the overnight return can serve as a proxy of the T+1 trading mechanism. The paper finds that the overnight return of the Chinese stock market is significantly negative, whereas those under the T+0 trading mechanism, such as China’s stock index futures, Hong Kong stocks, and major international indices, all have around 0 or positive overnight returns. T+1 trading mechanism has greater impacts on stocks with more divergent investor opinions, higher risk, more individual investor percentages, higher arbitrage restrictions, and less liquidity. The T+1 trading mechanism distorts the price generation mechanism of stocks. The paper contributes to the understanding of impact of trading mechanism on stock prices.