In order to study the influence relationship between the output voltage of the infrared detector made by the thermopile principle and the key structure size, to obtain a high output voltage, a microelectromechanical system (MEMS) Thermopile Infrared Detector based on circular structure was proposed. The size of the infrared detector is 1.8mm×1.8mm×0.35mm and the cavity size was 1.2mm as the research basis of modeling and simulation. Modeling the Infrared Detectors, by changing the absorption layer coverage length, thermocouple logarithm, the cold end, presence of etching rules hole size parameters of the key structure, such as the Infrared Detector thermoelectric heat simulation and path analysis, ultimately determine the optimal infrared detector simulation results, the simulation results show that by changing the Thermopile Infrared Detector size parameters of the key structure, The output voltage of the designed Infrared Detector is up to 125.08μV, which greatly improves the output voltage of the external Infrared Detector compared with the traditional four-terminal beam structure.