Collision caused by that multiple RFID tags try to transmit their identifiers through the shared wireless communication channel simultaneously is one of the key issues that affect the ubiquitous adoption of RFID system. In this paper, based on the stochastic distribution model, a simple but efficient tag population estimation method is suggested to work in the splitting tree collision resolution protocol, and the estimation accuracy is also discussed. Based on tag population estimation, the group of RFID tags to be identified is divided into multiple subgroups to be resolved in following slots. This group splitting process is performed recursively until that in each subgroup, there is zero or one tag, so all subgroups can be resolved and all tags can be identified. The performances of different splitting tree protocols are evaluated and some useful conclusions are achieved.