By replacing the first 3 dB coupler with a phase generating coupler (PGC) in the conventional Mach-Zehneder interferometer (MZI) electro-optic switch,a novel improved switch is designed. The structural model is presented,and the principle is described. The expressions of the amplitude transfer matrices are derived,and the compensating principle of the phase shift and the switching condition are analyzed. The parameters are optimized,and the characteristics are simulated,involving the propagation power,output power,output spectrum,insertion loss and crosstalk. Simulation results for the designed device show that,the push-pull switching voltage is 2.445 V,the switching time is 18.1 ps,the pass-band of the output spectrum can be increased to 110 nm,and the insertion loss and crosstalk are less than 2.24 dB and -30 dB,respectively,within the wavelength range from 1492 to 1602 nm. Our simulation results agree well with those of the Optiwave software based on the beam propagation method (BPM).