Conformal invariance and conserved quantity of Mei symmetry for Appell equations of nonholonomic system of Chetaev's type with variable mass are studied. The conformal invariance and Mei symmetry for Appell equations of nonholonomic systems of Chetaev's type with variable mass are defined under the infinitesimal transformation of group, and the determining equations of conformal invariance of Mei symmetry for the system are given. Then, the expression of the corresponding conserved quantity of the system is derived. Finally, an example is given to illustrate the application of the results.