Based on the Hertz equation, an equivalent film thickness method using spherical indentation was proposed to determine the modulus of thin films by means of modifying the mechanical model of flat cylindrical indentation. The FEM results verified by RW model show that the?error of the proposed model is less than?RW model when?the elastic modulus of film?is greater than that of the substrate; on the contrary, the results of the present method still agree well with the theoretic value while the indentation is much deeper. Therefore this model could be used to the instance that the indentation is more severe. In addition, the influences of yield strength of thin films and radius of the ball on the results were studied. It is found that the greater the yield strength of the thin films is, the smaller the error derived by proposed model is. At the same time, with the increase of the indenter radius, the error is greater under the same indentation depth. Furthermore, the influence of the radius on the modulus is smaller when the indentation is shallow. The proposed model is verified by indentation experiment on TiN/sapphire with Spherical indenter and Berkovich indenter