This paper presents a combination strategy to determine the optimal location of PV distributed generation units (PV-DGs) in terms of maximizing the power system voltage stability level. The voltage collapse power indices (VCPIs) is chosen to access the voltage stability level of a system. To eliminate the need of iterations, a new line power flow calculation method based on the line sensitivity factors (LSFs) is developed. It could precisely compute out VCPI without executing AC power flow program. Combined with the economic optimization software HOMER to determine the sizes and quantities of PV-DGs, the optimal buses to connect PV-DGs are selected by minimizing the sum of VCPIs. The proposed location strategy is validated by multiple IEEE test systems. The numerical simulation results demonstrate that the proposed method is accurate on VCPI calculations and has the decreased computation time compared with the Newton-Raphson power flow method. Through the continuous power flow results, it is verified that the optimal DG configuration selected by the proposed strategy could maximize the overall voltage stability margin of the system.