The overall structure design of a hydraulic driving type weightbearing exoskeleton was briefly described. Multiobjective optimization model was set up to minimize the force and the quality of the knee joint hydraulic cylinder.The linear weighted sum method in multiobjective optimization method was used to carried on the optimization, and the multiobjective optimization problem was transformed into a singleobjective optimization problem.The fmincon function and genetic algorithm of MATLAB were respectively used to optimize the model to make the stress value and the quality of the hydraulic cylinder greatly reduce. Therefore, it saves energy consumption and extends the life of the weightbearing exoskeleton drive system.