Distributed Generation (DG) access to distribution network the power may be transmitted from low-voltage power grid to high-voltage, causing adverse impacts on power grid. Among all kinds of factors, the power restriction is the main factor that affects the access of DG to distribution network. A mathematical model of maximum capacity of DG is built when reverse power node voltage and power flow constraint are considered and then the calculation method is introduced in this paper. It also analyzes the effect of DG on active power loss of distribution network. Considering the effect of holidays on power load, the proposal of adjusting reverse power constraint to increase DG capacity is given. The feasibility of the proposed method is proved by the example of distributed photovoltaic (PV) generation access to a 33-node 10 kV distribution network. This work is supported by National Natural Science Foundation of China (No.51722701) and Scientific and Technology Project of Guangdong Power Grid (No. 039900KK52150001).