The invention relates to a calculation method for the allowed capacity of DGs in the active power distribution network under the voltage constraint. The calculation method comprises the steps that (1) the access amount and places of the DGs in the active power distribution network are programmed; (2) DG access combinations and the operation modes of different DG access combinations are determined; (3) the access amount of DGs in periods and the generating capacity and load value of the DGs in each period are determined; (4) power flow optimization calculation is carried out on the access capacity of the DGs in all periods of each DG access combination; (5) the objective function of the maximal capacity of DG allowed by the active power distribution network is determined; and (6) the optimal DG access capacity of each access point is determined according to the objective function. The maximal DG access capacity is determined based on the power flow optimization calculation of the DGS in multiple periods, access of the DGs in the power distribution network is analyzed, the non-determinacy of DG output power of different periods and the dynamic change of load are taken into consideration, global searching optimization is carried out, and a DG optimization configuration scheme is obtained.