Aiming at application requirements of highfrequency electrooptic modulators, a PIN type electrooptic modulator based on SOI resonator has been proposed. Describing the resonance characteristic of microring resonator via the Scattering Matrix Method, combining the variation of effective refractive index of silicon resulted from carrier concentration changing, the plasma dispersion effect, analyzing the theoretical model of the microring resonator electrooptic modulator systematically. Based on the simulation and analysis of the crosssection optical field distribution of rib waveguide by Rsoft simulation software, a design of rib waveguide microring resonator with better performance of optical field confinement has been obtained. Furthermore, the performance of the PIN type diode for different doping concentrations has been simulated by Sentaurus TCAD simulation software. Finally, a blue shift of 58.74GHz is achieved from the theoretical model. It is demonstrated that the optimum design of the electrooptic modulator is reasonable and meaningful in further study of electrooptic modulator.