The invention discloses a firefly algorithm-based distributed power supply optimal capacity and position determination method. The method comprises the following steps of theoretical modeling of a distributed power supply distribution network, power flow calculation of the distribution network, calculation of the maximum penetration level, initialization of target firefly algorithm, updating of a firefly position, determination of a non-inferior solution set, updating of an external archived file, judgment of whether to reach the preset maximum iteration number, and outputting of a result. On the basis of minimum network loss, the basic firefly algorithm is improved, global search and parallel computing abilities of the firefly algorithm can be well used, and the optimal access capacity and the optimal position of the distributed power supply accessed to the distribution network can be searched; and compared with other methods, the algorithm is simple, the optimization speed is fast, the convergence accuracy is high, and the optimal access capacity and the optimal position of the distributed power supply can be better analyzed.