The invention relates to a power distribution network reactive power optimization method based on an improved NAGAII algorithm, and the method comprises the steps: S1, determining an optimization target, and building a target function; S2, determining the number of control variables and constraint conditions; S3, initializing control parameters of the improved NSGAII algorithm, and generating an initial parent population; S4, performing genetic operation on the parent population individuals, performing updating, generating new individuals to generate a test population, and calculating target function values and overall constraint violation degrees of the test population individuals; S5, enabling individuals in the parent population and the test population to compete to generate a temporarypopulation; S6, performing non-dominated solution sorting and congestion distance sorting on individuals in the temporary population, and selecting a new parent population; S7, judging whether the number of iterations is greater than the maximum number of iterations or not, if so, stopping iteration, and outputting a reactive power optimization result; and if not, returning to S4. According to the method, the problems that the original NAGAII algorithm is easy to fall into local optimum and the convergence speed is low are effectively solved.