The invention provides an optimization method for locating and sizing of a distributed power. The method comprises the following steps: establishing a multi-objective optimization model of the locating and sizing of the distributed power; defining constrains of the multi-objective optimization model; establishing a distributed power random output model and processing the distributed power random output model; establishing a load random output model; and carrying out locating and sizing of distributed power. According to the invention, with minimum network loss and maximum delayed investment benefits being as target optimization functions and by utilizing a two-step optimization method, the access location of the distributed power in the power distribution network and installation capacity are obtained, so that the positive effect of the access of the distributed power on the power distribution network is fully embodied and the optimization method can be used to evaluate economic benefit of the access of the distributed power to the power distribution network from the aspect of capacity-expanding effect.