In renewable-rich regions such as deserts, gobi, and sandy areas, weak local load and the lack of synchronous power sources often lead to voltage fluctuations and transient stability issues during large-scale photovoltaic (PV) integration and power delivery, posing significant challenges to system security. To enhance the voltage support capability of the sending system under disturbances, this paper proposes a dynamic reactive power compensation siting method that integrates both transient and steady-state characteristics. The method performs static hierarchical screening based on voltage stiffness, simplifies the candidate set using the Reactive Synergy Sensitivity Index (RSI), and further evaluates the voltage improvement effects under typical disturbance scenarios through transient response indicators, achieving a balance between accuracy and computational efficiency. Simulation results demonstrate that the proposed method effectively suppresses voltage overshoot and shortens recovery time under typical three-phase short-circuit faults. Compared with traditional methods based on single indicators, it shows better performance in terms of stability and cost-effectiveness, confirming its practical applicability and potential for wide adoption.