To solve the problem of penetration level calculation when a wide range of distributed photovoltaic (PV) is connected to distribution network, the influence of the distributed PV integration on the distribution network is analyzed firstly considering voltage stability and regional solar energy distribution. Then voltage constraints are deduced using custom matrix, and a penetration level calculation method based on matrix description is proposed to avoid flow iteration when uses voltage constraints to calculate penetration level. Generic data structure and matrix description are adopted to extend the calculation scale conveniently. Genetic algorithm is used to calculate the specific penetration level of each node and the penetration level value based on constrained voltage is got. Finally, taking the IEEE11 node system as an example, the proposed method is simulated and calculated. The penetration levels of the three scenarios, i.e. distributed PV access without considering extra restriction, evenly distributed access based on distance and evenly distributed based on nodes are obtained respectively, thus proposing ways suitable for large-area distributed PV access. This work is supported by National Natural Science Foundation of China (No. 51777166) and Natural Science Basic Research Plan in Shaanxi Province (No. 2014JM2-5077).