This paper adopts an EKOP model,VPIN model,and VWPIN model to measure the probability of informed trading( PIN) in China's stock market,and empirically examines the effect of PIN factors on asset pricing. It is found that the volume-weighted probability of informed trading( VWPIN) model based on clocktime developed in this paper combines the advantages of both classical PIN model and VPIN model. Meanwhile,the VWPIN modelcan conveniently estimate the information asymmetry over any time window during a trading day. Furthermore,the empirical results of the asset pricing suggest that PIN factor estimated by the VWPIN model is significantly and positively correlated with stock returns after controlling other pricing factors,which is consistent with the theoretical implications.