In this paper,the problem of waveform unsmoothness in RTM imaging is studied,and the influence of spatial and temporal sampling intervals on waveform smoothness is analyzed by using a simple model. The results show that the spatial sampling interval has great influence on the smoothness of waveform,while the change of temporal sampling interval cannot change the smoothness of waveform. The waveform unsmoothness can be solved by interpolating RTM image waveform in space by cubic spline interpolation. The validity of the method is verified by a complex model. At the same time,the seismic properties(instantaneous amplitude,instantaneous frequency and instantaneous phase)along layers of the RTM imaging are analyzed,and the results show that the waveform can improve the lateral spatial variation stability of seismic properties after smooth correction.