Olson considers that the key factor of collective public goods supply is the size of the group, which is small group more tend to supply collective goods than big group. But the theory of Olson can not explain some contrary facts: some big group is willing to supply public goods. Even in the same group, people are different in supplying public goods. Olson thinks that there are different operating principles, but we can not distinct big groups from small groups. So, we think that the key factor of collective public goods supply is members’ identity of the groups. If members’ identity of the groups is high, they will positive supply public goods, and vice versa.