Abstract: In the paper a optimum design method for hydraulic heavy load wrist of robot which works in a complex multi-obstacles circumstance is proposed.Several important objective functions presenting the work performance and construction compactness,such as linear cylinder length and maximum allowance pressure angle are given.Then optimum design process and result for 3 DOF heavy load hydraulic wrist of 155HP-1 robot is presented as an example.The construction of the wrist is designed specially and three revolute joints are arranged separately,but their axes are still intersecting.The concrete construction of the wrist is shown and it is optimium construction under this condition.