During a long time coherent interval, the maneuvering target may have multiple motion states, which would result in motion parameters change (MPC). In order to correct the MPC effect and achieve the coherent integration, a new coherent integration method is presented in this paper. Specifically, the piecewise function in terms of motion parameters of a maneuvering target is first utilized to construct the motion model. Then, a reference signal is introduced to remove the MPC effect. After that, GRFT is utilized to eliminate the range cell migration (RCM) and Doppler spectrum spread (DSS) effects and achieve the long time coherent integration. Additionally, considering the large computational cost, the time-frequency (TF) analysis is employed to estimate the change time of acceleration and the corresponding motion parameters in each state. Finally, simulation results demonstrate the effectiveness of the presented coherent integration method.