The invention provides a distributed photovoltaic power generation based power distribution network peak load control method. The minimum sum of distributed power supply investment and operating expense, line investment and operating expense, and maintenance expense is considered and taken as the start point; and expansion planning for connecting the distributed power supply to the power distribution network by using a genetic algorithm is carried out. When the distributed power supply is connected to a load node, the load and power flow of the node can be changed to further lower the load on the line, so that the load on the line can be higher than the planned and designed load; and meanwhile, the reasonable distributed power supply access can effectively lower the line loss and improve economic efficiency.