In order to improve the ability of the HVDC transmission system to resist subsequent commutation failure, subsequent commutation failure suppression method based on optimized current error controller parameters is proposed. Firstly, the mechanism of the effect of the extinction angle increment of the current error controller output on the subsequent commutation failure is analyzed. Besides, the slope of current error controller (CEC) is optimized offline by using deep reinforcement learning, leading to the proposed CEC control method of adaptive slope with offline optimization and online simulation. Finally, the effectiveness of the proposed suppression strategy is verified by using the CIGRE standard test model.