The invention relates to a double-energy X-ray spiral CT system for detecting liquid safety, which comprises a detecting device consisting of an X-ray source, a rotary table, a detector or an interlayer detector and a data acquisition unit, and a control part consisting of a microprocessor and a controller, wherein the front end of the detecting device is provided with the X-ray source; the X-raysource is the switchable high-voltage X-ray source or the fixed high-voltage X-ray source; the middle part of the detecting device is provided with the spiral lifting rotary table used for placing a detected liquid; the rear side of the spiral lifting rotary table is provided with the detector or the interlayer detector; the data acquisition unit is connected with the detector or the interlayer detector; the control part comprises the microprocessor and the controller connected with the microprocessor; the controller is connected with the X-ray source and the spiral lifting rotary table; and the microprocessor is connected with the data acquisition unit. The method comprises irradiation, detection, acquisition, comparison, and obtaining a detection result. The system can detect liquid density and equivalent atomic number and ensures to accurately judge liquid property.