The invention belongs to the technical field of aerospace measurement, and particularly relates to a bolt pretightening force measurement method. The method comprises the following steps: a ring washer is processed, a ring boss is respectively processed on the upper end surface and the lower end surface, and bosses on the upper end surface and the lower end surface have different diameters; four grooves are uniformly processed at a bending place of the washer, and strain gauges are respectively attached to the upper surface and the lower surface of each groove; a full bridge circuit is arranged to weld a wire on the washer; the washer is calibrated; in the case of measurement, the bolt sequentially passes through the washer and a butting surface, a nut is used for screwing, and the wire led out by the washer is respectively connected with a voltage-stabilizing DC power supply and a voltmeter; tightening torque is applied to the bolt, a pretightening force generated when the bolt is tightened is applied to the washer, a corresponding voltage is read in the voltmeter, and in contrast with a calibration certificate, a bolt pretightening force is obtained; the tightening torque is applied to the bolt in different grades, corresponding output voltage of the washer is measured in different grades, and through calculation, the pretightening force value measured by the washer is obtained; and a relationship between the bolt tightening torque and the pretightening force measured by the washer is fit.