A fault location method for a Web application system comprises the following steps: (1) building an expansion dependable matrix model: abstracting all fault points and available detection in the system, determining correlation between the fault points and the available detection, and describing the built expansion dependable matrix model; (2) carrying out detection: sending a detection request to a target Web application system, analyzing returned results, determining success or fail of the detection, and obtaining detection results assembly as symptom data for fault rational analysis; and (3) performing fault rational analysis: performing failure detection of related fault points to filter for fault points with fault probability base on the expansion dependable matrix and the symptom data detection results assembly; performing success detection of related fault points to exclude fault probability; and analyzing the probability of each fault in the fault point assembly obtained by filtering, and arranging in the sequence from high to low.