The invention provides an automobile chassis part weight reduction method based on multi-body dynamics and a topological optimization technology for the purpose of solving the problems that in existing automobile designs, a clear and feasible weight reduction method is unavailable, and an automobile chassis part still has a large weight reduction space. The automobile chassis part weight reduction method comprises the following steps: step 1, a finished automobile multi-body dynamic model and an object part finite element model of an object automobile type for weight reduction are established; step 2, multiple typical working conditions are selected, and an equivalent static load borne by an object part under each typical working condition is extracted; step 3, the equivalent static loads extracted in the step 2 are used as optimization boundary conditions, a flexibility weighting coefficient of each typical working condition is selected, the minimum total weighting flexibility serves as an objective function, and topological optimization is conducted with a constraint function including modality and stress; step 4, a threshold value is selected for a topological optimization result, and the position of a material to be removed is guided. The automobile chassis part weight reduction method based on the multi-body dynamics and the topological optimization technology combines a fatigue strength design with a static strength design, thereby having high reliability, portability and operability and being capable of effectively shortening the development cycle.