To predict the behaviors of the whole Micro-electro-mechanical System(MEMS) including MEMS devices and circuits, a prototype system for co-simulating MEMS devices and circuits was established. Firstly，the common characteristics of MEMS system-level simulation and analog circuit simulation were studied,and the principle and the method of co-simulating MEMS devices and circuits were presented. Based on the circuit simulation platform Zeni VLG, the frame of the prototype system was established. Then, two parametric model libraries which were essential for the prototype system were also established, respectively, according to the modified nodal analysis method and analog circuit behavioral modeling method. A seesaw accelerometer with an open-loop circuit and a closed-loop circuit was used to verify the system and the models.By comparing to the commercial software SaberTM, obtained results indicate that the relative error is 2.1% in the open-loop simulation. The simulation results show that the prototype system could handle co-simulations of MEMS devices and circuits effectively, and has a high accuracy.