The invention discloses a mobile vehicle detecting system which comprises a mobile device, a driving device, a ray source, a rotary table, an upright column, a transverse detector beam and a vertical detector beam, wherein the driving device is used for driving the mobile device to move during scanning and detecting period, the ray source is used for emitting rays, the rotary table can be arranged on the mobile device pivotally, the upright column is arranged on the rotary table, the transverse detector beam is connected with the upper end of the upright column and provided with a detector array, and the vertical detector beam is generally vertical to the transverse detector beam and provided with a detector array. The mobile vehicle detecting system further comprises an auxiliary support device arranged at the bottom of a chassis frame and at one sides of the transverse detector beam and the vertical detector beam, the auxiliary support device is used for supporting the chassis frame in an auxiliary way so as to keep the chassis frame balance when the transverse detector beam and the vertical detector beam are in an extension position. The mobile vehicle detecting system has the advantages of simple structure, convenience for processing and debugging, wide scanning range, light vehicle weight and low manufacturing cost.