In information field, one famous assertion is that performance of centralized fusion must be better than that of distributed fusion and also is optimal. It has been proven that this assertion is correct as single model filter, such as kalman filter, is adopted in fusion system. However, in case of maneuvering target tracking, in which multiple model filter, such as IMM filter, is usually applied in fusion system, is above assertion still valid? With doubtful attitude, this problem is investigated in the paper, three centralized fusion algorithms and two distributed fusion algorithms when IMM is used are presented, and simulations are made in different kinematic sceneries. Simulation results indicate that, as IMM filter is used in fusion system, performances of centralized fusion are not always better than those of distributed fusion. Analyses about this surprise result are also given in last section of the paper.