This paper presents an augmented probability of informed trades ( APIN) ，and evidences its better ability to measure the informational asymmetry in China’s stock market than PIN． Information would determine the profit of stock tradings in a transitional stock market with insider-trading and a strict restriction for short-sale． In this case，“no news”investors would prefer more sales to buys to avoid loss． On one hand，investors without any news would attribute themselves to “inferior participants”in the trading game，meaning that“no news”is bad news; then they are apt to sell stocks． On the other hand，the sales ratio of“no news”investors would boost with the rise of informational asymmetry． Since“no news”investors always ask for higher bid prices than investors with real“bad news”，their sales would lead to a number of reductions of bid-ask spreads，resulting in significantly negative APIN-Spread connections and undervaluation of PIN for information asymmetry． In all，compared with PIN，APIN depicts the information asymmetry of China’s stock tradings more clearly，and better illustrates the case in which“no news”is“bad news”．