The invention discloses a method of detecting cascading failure in an AC-DC hybrid system. The method comprises steps: the AC-DC hybrid system is initialized; failure is set; load flow calculation is carried out; whether the load flow converges is judged, if yes, voltage of each DC commutation bus in the AC-DC hybrid system is checked, a DC commutation bus whose voltage is smaller than a preset value is locked, and the next step is carried out; if not, a part of loads are added or reduced, and load flow calculation is carried out again; whether a line is broken is judged, if yes, failure is set again; if not, loss load is calculated, the cascading event probability is obtained, and classification and confirmation on cascading failure in the AC-DC hybrid system are carried out. The method of the invention has the advantages that cascading failure can be effectively detected, and the amount of calculation is small.