The terahertz filter is an important component of the terahertz system, which is difficult to be designed quickly and accurately. Based on the co-simulation of Genetic Algorithm(GA) and finite element method, a fast and accurate design method of terahertz filter is realized. The HFSS-MATLAB-API script library is utilized in the design, which not only adopts the accuracy of HFSS for field simulation, but also reduces the blindness of tentative optimization by genetic algorithm in MATLAB. A 210-230 GHz band-pass filter is designed by this method. The measured results show that the in-band insertion loss is less than 0.6 dB and the out-of-band rejection is more than 30 dB. The accuracy of the method is verified.