The invention discloses an extraction method of a contour line of a clearance distance between an electric transmission line and the ground surface based on point cloud data. Through the steps of point could acquisition, point could classification, lead wire fitting, span length partition, clearance distance calculation, distance minimum point extraction, clearance distance minimum point projection and conversion, contour line generation and the like, a contour line of the clearance distance between an extra-high voltage direct-current electric transmission line and the ground surface of a line corridor below the extra-high voltage direct-current electric transmission line is extracted, the height of the contour line indicates the clearance distance between a lead wire and the ground, andconditions of the distance between the lead wire to ground objects below the lead wire under different working conditions of static or wind deviation can be visually displayed; and meanwhile, comparison of multi-period data of the ground surface of the line corridor can be realized based on the contour line, areas with changes of the ground objects below the lead wire or trees are discovered, andreference is provided for the control over the line corridor. According to the extraction method of the contour line, the design is scientific and reasonable, different working conditions can be fullytaken into account, and the minimum clearance distance between the whole section of the electric transmission line lead wire and the ground surface so as to realize the control over tree barriers.