Frequent track initiation often happen when radar tracks dense formation targets. Due to the need of merging formation members' tracks, a formation target recognition algorithm based on sliding window track association is proposed. A two-track formation recognition model based on weighted track association decision is given firstly. Then, circulated threshold decision is used for multiple tracks' formation separation. At last, sliding window of multi-time formation recognition confirming and formation merging are undertaken to generate the merging track. Simulation results show that: the algorithm can recognize formation target and generate merging track whether the formation is maneuvering in parallel or is making crossing moving in which frequent track initiation happens.