The radial deformation coefficient（ RDC） is one of the important parameters that influence the elastic deformation of flexspline（ FS）,the double circular arc tooth profile（ DCTP） is selected as the tooth profile of harmonic transmission FS,the influences of RDC on conjugate exist domain（ CED）,conjugate tooth profile（ CTP）,the locus of meshing are researched by using MATLAB based on the envelope meshing theory of harmonic drive（ HD）. The results show that RDC not only has evidently influence on the radial deformation of FS tooth that near the long axis and short axis of wave generator（ WG）,but also the tangential deformation and normal angle of FS tooth that near the transition segment between the long axis and short axis of WG; with radial deformation coefficient decreases,the CED increases with the RDC increase,while the blank area between the CED is decrease,moreover,the CTP of CED one shifted upward,while the CTP of CED two move shifted downward,the effectively CED and effectively CTP are found. Furthermore,reasonable choice of radial deformation coefficient is one of the important ways to avoid the meshing interference of HD and improve the meshing performance of HD.