Large-scale integration of distributed photovoltaic (PV) systems into distribution networks can easily lead to line overloads, voltage instability, and other issues. The existing PV hosting capacity optimization methods, which mainly focus on economic performance, are often insufficient to ensure voltage stability in distribution networks. This paper proposes a quantitative method for assessing the hosting capacity of distributed PV in distribution networks based on static voltage stability margin (SVSM). First, an analytical expression for a static voltage stability index, characterized by PV output power, is derived, revealing a quadratic function relationship between distributed PV output and the static voltage stability index. Then, with the objective of maximizing PV integration capacity, a hosting capacity quantification model is established, considering constraints such as SVSM, distribution network line loss rate, voltage magnitude, and reactive power compensation devices. An improved adaptive genetic algorithm is used to solve this nonlinear model. Finally, the IEEE 33-node system is used as a case study to validate that the proposed method can effectively guide distributed PV deployment in distribution networks.