The silicon-based ultra-compact microring resonator in the terahertz communication window was designed.According to the transfer matrix method and the coupled mode theory,the transfer function of the microring resonator was calculated,and the critical coupling conditions of microring resonator were obtained by analyzing the waveguide coupling coefficients.3D finite-difference time-domain method is used to analyze the performance parameters of microring resonator,and the obtained results were compared with that of the cascade dual microring resonator.The results show that a free spectral rang of the microring resonator is 27 GHz and an insertion loss is 0.3 dB.And the spectral shape factors of two kinds of microring resonators are 0.16 and 0.52 respectively.That means cascade dual microring resonator result in flatter top resonance and higher roll-off vertical degree.