Abstract: A tracking algorithm with adaptive association gate is proposed to the maneuvering target tracking in clutters. The algorithm is based on conventional Interacting Multiple Model Probabilistic Data Association (IMM-PDA) algorithm, and the target is assumed to change its moving mode with the maximal maneuvering level at current or heretofore moments when there is no valid measurement in the association gate. The innovation covariance used to determine the association gate is modified according to the predicted measurement in the maximal maneuvering hypothesis and the actual one. The association gate is enlarged step by step appropriately to gate the target measurement as far as possible. Simulation results show that, the proposed algorithm can improve the tracking loss rates of maneuvering target effectively without decreasing tracking precision or increasing computational complexity.