Provided in the invention is a design method for access of a flexible multi-state switch to a distribution network. On the basis of simulation of a multi-scene power flow, distribution network weak positions including distribution network node voltage limiting exceeding and line load heavy loading and the like after access of a distributed power source are calculated and analyzed and a flexible multi-stage switch access location is determined; a system optimization model of access of the flexible multi-stage switch to the distribution network using economic cost minimization as an objective function is established, wherein the objective function includes a yearly conversion cost and a system operation loss cost of initial investment of the flexible multi-stage switch and various constraintconditions are met; with an improved particle swarm optimization method based on a genetic algorithm (GA-PSO), an optimization design model including discrete variables and continuous variables of the flexible multi-state switch is calculated, mixed coding is carried out on the complicated discrete variables and continuous variables, and crossover and mutation operations of the genetic algorithmare introduced into a particle swarm optimization method for improvement; and thus an optimization design plan for access of the flexible multi-state switch to the distribution network is obtained byoptimization calculation.