This paper points out the deficiencies for economics to explain industry cluster and tries to study it from the viewpoint of entrepreneur's social networks.Based on the relationships between environment,networks and behaviors,this paper makes two conclusions from the applied study by examining the model of "Casting Net" in endogenic cluster:(1) Strong tie plays the most important role in entrepreneur "casting net";(2) Path dependence in individual behaviors influences the processes and results of entrepreneur "casting net".