This study is a comparative analysis of the effect size to evaluate the importance and difference of the effect of the play therapy which have theoretical background on the externalizing problem behavior, using meta analysis method. This study consists of three subjects : First, the overall average effect size of play therapy on the externalizing problem behavior, Second, the effect size of each theory, Third, the effect size according to the other variables : the subject age, disability status, the number of the subjects and the number of the total session. The 54 published theses of master and doctor (period 2005~2014) were chosen, which are all experimental studies based on quantity analysis, in order to satisfy the condition of meta-analysis. using externalizing problem behavior as a dependent variable. The main results of this study are as follows. First, the overall average effect size of the play therapy which have the theoretical background on the externalizing problem behavior is 0.77 which is high level in terms of Cohen criteria. Second, the child-centered play therapy showed 1.13, the highest effect level among all studied play therapy according to the theoretical background. Lastly, the effect size according to the other variables showed 2.27 in adult group, 1.53 in disabled group, 3.70 in 2-3 members group, 2.37 in 1-8 session group. As a conclusion, this study shows that the play therapy is so effective when it has clear theoretical background.