The invention discloses a failure detecting method for the zero-crossing trigger circuit, which comprises the following steps: 11), testing whether the time interval of the zero-crossing signal exceeds the maximum time interval T1 of the zero-crossing signal; if exceeding, then going to the next step; if not exceeding, then going to the step 13); 12), going to the step 14) if the zero-crossing signal circuit works abnormally; 13), if zero-crossing signal circuit works normally, outputting driving signal to the high-power semiconductor device of a main driving loop, and then going back to the step 11); 14), performing failure treatment. Furthermore, the step 11) is as follow: 21), resetting the calculagraph CT and beginning timing; 22), receiving the zero-crossing trigger signal; if existing zero-crossing trigger signal, then going back to the step 21); if not existing zero-crossing trigger signal, then going to the step 23); 23), checking whether the timing time of the calculagraph CT is more than T1; if the timing time of the calculagraph CT is more than T1, then going to the next step; otherwise, going back to the step 22). The invention enables the user to judge whether the failure happens in the zero-crossing trigger circuit accurately.