Silicon photonics is a novel technique for high scale optical/electronic integration,with which most kind of optical devices can be achieved. Silicon microring-based electro-optic modulator is one of the most important devices for photonic integration. Compared to the amplitude modulation,optical phase shift keying (PSK) is a better choice for the optical power efficiency. The Mach-Zehnder modulator (MZM) is usually used to obtain the phase shift keying modulation,but its bulky size and producing technic make it hard for the LiNbO3 MZM to be used in the optical integrating system. The μm-sized silicon microring modulator holds the capability of mass-produce and optic integration. Here the silicon microring modulator is used to achieve optical phase shift keying. The coupling mode and 1-D finite difference time domain (FDTD) are adopted to analyze its characteristics and optical-fiber communication. The results show that the signal Q-factor of the silicon microring modulator can be larger than 20 dB,which means the error-free communication is reachable.