An asymmetric Y-branch Mach-Zehnder interferometer electro-optic switch with microstrip line electrode is designed and fabricated.Through using two pairs of asymmetrical Y-branch waveguides as the splitter and coupler, respectively, a phase difference between the two MZI arms, and then the bias-free function can be realized.The switching time is measured to be ~100 ns.The reliability performance of the device is analyzed and measured, too.