Yan, L (reprint author), CAS, Inst High Energy Phys, Beijing 100049, Peoples R China.
In this paper, the kinematic fitting with the Lagrange multiplier method has been studied for BESIII experiment. First we introduce the Lagrange multiplier method and implement kinematic constraints. Then we present the performance of the kinematic fitting algorithm. With the kinematic Fitting, we can improve the resolution of track parameters and reduce the background.