Abstract: Two?way wave equation based on reverse time migration ( RTM) has such advantages as simple principle,no angle restric?tions,suitability for the model of arbitrary speed changes,and correct imaging for all kinds of waves.Nevertheless,the adoption of the cross?correlation imaging condition can produce low?frequency noise problems.Based on analyzing the mechanism of the low frequency noise,the authors put forward an effective wave field separation denoising method,in which the source and the receiver wave field are separated into different directions of one way wave component,and only cross?correlation imaging is conducted on the effective path of the component,so as to achieve the purpose of removing noise. The results of the model test and comparative study of the denoising effects of Poynting vector filtering,Laplasse filtering and wave field separation show that the wave field separation method is relatively effective in these three methods.