The tracking accuracy of conventional Adaptive Interactive Multiple Model (AIMM) algorithm is poor in the process of maneuvering target tracking by passive radar. In combination with the characteristics of passive radar, the improved Adaptive Transition Probability Matrix-Interactive Multiple Model(ATPM-IMM) algorithm is proposed. Based on the ATPM-IMM algorithm, this algorithm uses the adaptive control window to revise the transition probability matrix again. It can automatically switch the maneuvering model according to the maneuvering situation of the target and improve the matching probability of real model. Simulation and experimental results show that the proposed algorithm can effectively improve the tracking accuracy of passive radar to maneuvering targets.