The invention discloses a detection method for filter failure of a dual-clutch transmission hydraulic system. The detection method comprises the steps of vehicle starting, judging of the condition that transmission oil temperature is larger than the set value, gear in-place quantity detection when only one gear is in place, gear shifting request judging within set time, oil charging of a non-working clutch, pressure difference calculation, filter fault judging and filter failure determining. According to the detection method, under the circumstance that a mechanical structure is not changed and an outer sensor is not added, a method for detecting the filtering ability of a filter in real time is achieved, during filter failure, a signal can be identified and sent in time, and further pollution to the transmission hydraulic system is avoided. Meanwhile, according to the detection method, a sensor in an original hydraulic system is used, the outer sensor does not need to be added, and thus the design change and production cost of hardware is saved. In addition, key parameters can be calibrated according to differences of the characteristics of different transmission hydraulic systems, and universality is high.