The purpose of multi-radar echo band fusion is to expand the signal bandwidth and improve the range resolution. Due to the difference of multi-radar space positions and the initial phase of echo, the phase Angle difference is linear phase and fixed phase. Therefore, solving the phase mismatch is the premise and focus of bandwidth fusion. The disadvantage of the existing phase-coherent registration method is that the phase-coherent registration accuracy is low at high noise level. Based on the geometrical diffraction theory (GTD) model, the algorithm analyzes the influence of non-coherent factors on the target echo, and uses the global minimum entropy criterion as the cost function to estimate the linear phase. According to the influence of fixed phase on the target scattering center parameters, a linear least squares method for correcting the pole subspace is proposed to estimate the fixed phase. The simulation results show the advantages and feasibility of the proposed algorithm.