Abstract: On the basis of Mei symmetry of Appell equations for nonholonomic systems with Chetaevs type in dynamics of relative motion,its conformal invariance and relative Mei conserved quantity are further studied.By introducing the infinitesimal transformations of groups and their generating vectors,the definitions of Mei symmetry and conformal invariance of Mei symmetry of Appell equations in the system are given.Necessary and sufficient conditions of which the system has both Mei symmetry and conformal invariance of Mei symmetry,and Mei-conserved quantity deduced directly from Mei symmetry in the system are gained.An example is given to illustrate its application.