Optimistic bias means people have a tendency to think that positive evens are more likely to happen to themselves and negative events are more likely to happen to other people. This research used the method of the Implicit Association Test to explore the implicit effect of optimistic bias. The subjects consisted of 60 college students. The data of IAT indicated that the mean reaction time in compatible test is shorter than one in incomaptible test signifcantly (t=-8.06, p<0.000), which means that participant tended to associate self with positive events and associate others with negative events. To explore further, we transformed the difference of reaction time between incompatible test and compatible test into D score as the indicator of implicit effect of optimistic bias. The mean D score is 0.47, One-Sample T Test showed that D score was above 0 (t=10.226，p<0.001),which suggested that there was significant implicit optimistic bias. However, there was no siginificant difference between sex although D score of female was less than male’s.