The present invention relates to a method and system for optimizing the joint hinge point position of a hydraulic tandem mechanism based on lightweight. The method comprises: determining rotational load characteristics of each joint in the hydraulic tandem mechanism using dynamics simulation software based on said end load characteristics and said structural parameters of the tandem mechanism; establishing a fixed coordinate system between two adjacent rods in each joint and a joint global coordinate system, and determining the relationship between hinge point coordinates, joint rotation angle and joint drive force arm of each joint; calculating linear load characteristics of each joint according to said rotational load characteristics and said joint drive force arm to calculate hydraulic cylinder structural parameters and hydraulic oil source flow rate for each joint; determining a lightweight index for the joint hinge point position of the hydraulic tandem mechanism according to said hydraulic cylinder structural parameters and said hydraulic oil source flow rate; solving the coordinates of each joint hinge point of the tandem mechanism corresponding to the minimum of said lightweight index, using said lightweight index as a fitness function, so that the overall weight of the tandem mechanism is minimized.