<FONT face=Verdana>A modeling method of throughput in Concurrent Multipath Transfer (CMT) environment is proposed and a simplified algorithm is also given under the premise of accuracy. The increase mechanisms of congestion window are analyzed and interpreted based on the features of different transmission phases. The model estimates the throughput according to the changes of round trip time and congestion window. Simplified algorithm can decrease the complexity sharply when we implement our idea on Matlab platform. And the agreement of calculation results and simulation results is satisfactory.