A study is conducted on the transient synchronization stability of a hydropower and photovoltaic power generation system transmitted via voltage source converter high voltage direct current (VSC-HVDC) considering current limitations. Firstly, accounting for the current-limiting control strategies of photovoltaic inverters and flexible rectifiers during faults, a mathematical expression for the active power output of hydro-generating units before fault clearance is derived based on Thévenin′s theorem. Secondly, leveraging the equal area criterion, an analytical formula for the critical clearing angle of the transmission system is deduced. This critical clearing angle served as a key indicator for evaluating the transient synchronization stability limit of the system. The influence of parameters such as the saturation current angle of photovoltaic and flexible converter stations, as well as the hydro-photovoltaic power ratio, on the transient stability of the transmission system is systematically assessed. Subsequently, an optimal control parameter tuning scheme is proposed to enhance the system′s transient synchronization stability. Finally, time-domain simulations verify the accuracy of the analysis on factors affecting transient synchronization stability and the effectiveness of the proposed optimal control parameter tuning method.