The invention discloses a borehole gap three-dimensional contour high precision scanning detection method. The method comprises a step of obtaining coordinates of scanning points and lengths of scanning lines on scanning planes of different depths, a step of setting a cylindrical projection surface, a step of carrying out insertion compensation on a projection point on a projection ring, and a step of carrying out insertion compensation on scanning points which are on the scanning planes of different depths and have same corresponding scanning line angle. The invention also discloses a borehole gap three-dimensional contour high precision scanning detection device which comprises a borehole detector which comprises a calibration part, a scanning part and a sealed shell. The calibration part comprises a calibration laser sensor, a plane transmission plate, a plane reflector and a linear motor. The scanning part comprises a stepping motor, an electronic compass, a rotating cavity and a scanning laser sensor arranged in the shell. The method and the device have significant improvement in the aspects of depth, environment, breadth, precision and the like of borehole gap detection and have broad application prospects.