Abstract: With the increasing penetration of distributed photovoltaic（DPV）, the proportion of traditional energy units continues to decline, resulting in a reduction of inertia and primary frequency regulation capabilities in power systems. Therefore, it is crucial to explore the frequency support capabilities of DPV in low-inertia systems. On this basis, first, this paper proposes an improved frequency active support method for voltage-type DPV-virtual synchronous generator（DPV-VSG） with variable reserve rate to enhance the system inertia, reduce the response delay, and improve the ability of DPV for active participation in system frequency support. Then, an optimal selection model for setting the power and frequency parameters based on the transient search optimization（TSO） algorithm is proposed to solve the optimal initial reserve power and best frequency regulation parameters of DPV, which improves the limitation of fixed photovoltaic initial reserve power. Finally, the proposed model is applied in a singlegenerator model and an actual distribution station area model with high penetration of DPV to verify its effectiveness.