In view of the low fidelity of existing thoracic simulator, a new type of machinegas composite thoracic simulator was developed. The mathematical models of the main sternum simulator and the rib simulator were established respectively. The effects of the radius and height of the simulator, the thickness and width of the leaf spring, the pressure in the simulator cavity and the compression displacement on the stiffness characteristics of the thoracic simulator were simulated, and the validity of the model was verified by experiments. The results show that by changing the pressure in the cavity of the simulator and the structural parameters such as the radius and height of the simulator and the thickness and width of the plate spring, the thoracic stiffness of patients with different ages and genders can be simulated respectively. The research results can provide a reference for the design of a new type of cardiopulmonary resuscitation teaching simulation device.