This paper employs agent-based modeling to study the impact of the T + 0 trading mechanism on market quality. The artificial stock market is built up according to the investor characteristics and market microstructure of Chinese stock markets. The experiment results show that when compared to T + 1, T + 0 increases pricing efficiency and market liquidity, and reduces market volatility, which in turn improves market quality. The reason is that T + 1 does not allow investors to sell when they have observed large changes in the fundamental value, so that they need to sell in the next opening session, which in turn generates large price impacts and high volatility; while T + 0 solves this problem since the large change of fundamental value can release in intraday transactions, and the actively intraday order submission also increases market liquidity. The results suggest that T + 0 can be applied in EFT markets of large stock indexes as a pilot project.