The invention discloses a detection tool and a detection method for a belt buckle fault of a passenger vehicle safety belt. The detection tool comprises a controller and a safety belt buckle, wherein the controller is provided with an external leading wire which is used for connecting with an original vehicular belt buckle harness socket; the types and positions of the belt buckle fault are judged according to the light-on or light-off of an indicating lamp on the controller. According to the detection tool and the detection method for the belt buckle fault of the passenger vehicle safety belt, the controller is used for replacing an original vehicular safety belt buckle detection loop; under the condition of not launching a vehicle, the safety belt buckles of all seats can be directly detected, the pertinence is strong, and the detection process is intuitive, quick, accurate and effective; the fast diagnosis is conveniently performed by maintenance staff in automobile 4S shops, and the maintenance time and cost are reduced.