Abstract: There is a projective point in the earth surface along the normal direction of the dipping interface for a common conversion point of three dimension PS-wave exploration.The essence of sorting CCP gathers is to calculate these proportions of the distance from shot to projection point and from receiver to projective point varies with azimuth.When the interface is dipping,these proportions are determined by the parameters including dip angle,dip direction,normal depth,azimuth and ratio of P-wave velocity and S-wave velocity.How do these parameters control these proportion dependences and affect the determination of common conversion point gather? What degree would they bring? In this paper,we will try to answer these questions by calculating some special models.The results show that it could cause disorder and error image of conversion wave gathers if we omit the influence of slanting interfac.