This paper investigates the informed trading in Chinese stock markets by a natural experiment of the PBC's interest rate cuts and reserve requirements rate( RRR) cuts. The empirical evidence shows that the return by opening price，volume per trade and the probability of informed trading appear a significant growth，whereas the volatility and the number of trades dramatically drop in the trading day prior to the PBC's interest rate cuts and RRR cuts. Moreover，the probability of informed trading increases more considerably in some stock sets such as the stocks with higher information asymmetry and the stocks from banks，securities，real estate industries which benefited more directly from the monetary policies. Our study also finds that prior to the release of interest rate cuts and RRR cuts，the volume and proportion of the big trades rise significantly，and the probability of informed trading both in big and small trades is also higher than in the normal situations. These results indicate that Chinese stock market has informed trading during stock market crash. Some rich investors use the insider information to trade stocks and get additional revenue in the market before the information significantly leaks to other rich investors and individual investors.