A modular bed-type gait rehabilitation training system was proposed aiming at the problem of inconvenience and high cost of existing rehabilitation training robot. The system consists of a bed with adjustable tilt angle, two leg motion auxiliary mechanisms and a foot support mechanism. The modular design can make it easier to use. Cam-connecting rod mechanism was used to simulate the movements of thigh and calf in order to generate normal walking gait. A human-machine coupling model was built and the kinematic analysis was carried out. The kinematic relationship between the mechanism and human lower limbs was obtained as the basis of parameter optimization and structural design. MATLAB was used to optimize the parameters of the model and get their optimal values, aiming at increasing adaptability of the mechanism to the patients with different body types. Experimental results showed that the maximum error of hip angle between the measured result and the standard result was less than 5.2°, the maximum error of knee angle was less than 6.7°, which demonstrated that the presented mechanism can adapt personal difference and it’s feasible to carry out rehabilitation training with this system.