The invention relates to an automobile chassis key structural member structure optimization design method. The method comprises: step one, determining chassis key structural member performance indexes; step two, establishing a suspension multi-body model, and calculating load of each connecting point of the chassis key structural member; step three, establishing a finite element initial design domain suitable for topological optimization design of the chassis key structural member; step four, establishing a topological optimization mathematical model; step five, iteration solving; and step six, acquiring a topological optimization design result of the chassis key structural member. The automobile chassis key structural member structure optimization design method is different from traditional design methods, combines a connecting point load decomposition technology and a nonindividual body topological optimization technology, reflects design requirements in an optimized mathematical model, enables a designing scheme to meet design requirements more accurately and comprehensively, is suitable for novel chassis key structural members which are high in rigidity, strength and light weight level, and has great significance on earlier stage concept design of car chassis.