A novel method for simultaneous measuring piezoelectric coefficient and electro-optical coefficients of crystal material is proposed by utilizing the ultrahigh modes excitation from a symmetrical metal-cladding optical waveguide. The method can be directly used to calculate the electro-optic coefficient and piezoelectric coefficient by shift of the reflectance curves at different voltages. The theoretics and experiment results all indicate that this method has an excellent performance, such as high compact, low insert loss, no moving parts, high reliability and so on, which promises an application prospect in optical devices in electro-optic coefficient and piezoelectric coefficient.