A fast search method and system for cascading failures in hybrid AC/DC power systems. The fast search method for cascading failures in hybrid AC/DC power systems includes: Determining the initial failures and forming a failure set of the first-stage failure, setting the DC blocking or the failure level reaching the threshold as the search stop condition; Judge the cascading failures in the failure set of the current stage can trigger DC blocking, if a cascading failure can trigger DC blocking, store the DC blocking failure as the next-stage failure. Otherwise, cascading failures are searched on the AC side and the failure set of the next stage is determined based on the pruning search method and the outage risk value; If the search stop condition is satisfied, stop the search, otherwise, the number of failure stages is increased by one and return to judge the cascading failures to continue the search.