For the HVDC transmission system built in the real time simulation platform based on RTDS, the conventional PLL technology can not realize the precise control of the trigger pulse of the converter valve, which is not conducive to the fault reconstruction of the actual HVDC project. Based on the principle of the instantaneous PLL control system, a high precision PLL modeling method is proposed, and high precision tracking measurement of power system frequency is realized. According to the actual operating conditions, the complete simulation model of the control system for Yun-Guang UHVDC Project is built based on the RTDS simulation platform and the simulation test example is designed. The experimental results show that the simulation waveform is highly consistent with the actual engineering records, and the simulation modeling method is effective and feasible.