Continuous commutation failures of line-commutated high-voltage direct current converter caused by AC faults lead to the blocking of HVDC-link. This may seriously threaten the stability of post-fault power system. Therefore, a collaborative emergency control strategy making use of DC power support is presented to guarantee transient stability after HVDC-link blocking. Firstly, the control enabling criterion is defined based on the variation characteristics of the phase trajectory slope during the first swing, while the analytical equation between the needed control quantity and the system parameters is derived. Secondly, the mathematical relation between the provided control quantity and the number of HVDC-links participating in the power support is deduced, and the participation sequence is determined on the basis of the post-fault stable equilibrium points. Additionally, the time delay of the whole implementation is considered. Finally, the effectiveness of presented control strategy is validated using the improved IEEE 68-bus AC/DC hybrid power system.