Abstract: At present, there are few researches on the response characteristics of control and protection system for DC transmission during the out-of-step oscillation of AC systems in large-scale AC/DC hybrid power grid. This paper analyzes the response characteristics of the control and protection system for DC transmission with a strong oscillation in AC grid of the large-scale AC/DC hybrid power grid based on PSCAD simulation and real-time digital simulation（RTDS）. In the simulation, a real AC grid, a fictitious AC grid, and single-and multi-infeed DC transmission systems are set up. The simulation results show that the DC transmission system will not be blocked in the first 2 cycles of oscillation so that the stability control system has sufficient processing time. There is a difference in the blocking time of the two poles caused by the non-linear characteristics of the DC control and protection system, which helps to avoid the simultaneous blocking of double circuits and two poles. During oscillation,the adjustment of the DC control and protection system and commutation failure will cause the DC transmission power to fluctuate greatly.