Abstract: The ultra-compact microwave photonic filter based on silicon-on-insulator microring resonator was designed to increase the integration density of microwave photonic devices and enlarge the free spectral range. According to the coupled mode theory of waveguide optics, the optical intensity transfer function of the microring resonator with parallel-coupled structure was deduced and the transmission spectrums were simulated numerically. The results show that when the radius of resonator of resonator is 0.79 m, the straight waveguide width is 0.3 m and the ring waveguide width is 0.25 m, the filter with full wave at half maximum(FWHM) of 7 nm can be achieved, which also has an exceeding free spectral rang 140 nmof and an insertion loss less of 0.5 dB. The performance of this filter can meet the requirements of coarse wavelength division multiplexing system.