The blocking of large-ampacity HVDC or the tripping of the AC transmission line after an accident will cause power flow transfer sharply and increase the risk of cascading faults in AC/DC hybrid power grid. Therefore, it is needed to take reasonable safety control measures to prevent the spreading of the accident in time. An overload control strategy for AC/DC hybrid power grid is proposed. This strategy brings the dynamic electro-thermal characteristics of the conductor into the safety constraints to fully excavate the short-time overload capability of transmission lines and then coordinates the active power adjustment of generators, power transmission adjustment of HVDC, and load shedding measures to realize the dynamic optimal power flow control associated with time. The optimization control model takes minimum total cost as the objective function, which can quickly obtain the economic and reasonable overload control scheme through selecting control variables, to effectively prevent cascading tripping in AC/DC hybrid power grid. Finally, compared with the control methods by adopting different line safety constraints and different optimal variables, the effectiveness and superiority of the proposed strategy are verified through case studies on the modified IEEE 39-node power systems. This work is supported by Fundamental Research Funds for the Central Universities (No. SWU119039) and National Key Research and Development Program of China (No. 2016YFB0900600).