The invention discloses a power transmission line modeling method used for net distance measurement and a distance measurement device thereof. The modeling method comprises the following steps that 1) the distance measurement device is installed below a suspension string, an endpoint O is determined, an auxiliary distance measurement device is installed on a lead to be measured, two endpoints A and B are determined through movement of the auxiliary distance measurement device, and length L1 of a line segment OA, length L2 of a line segment OB, an inclined angle theta1 between the line segment OA and the horizontal plane and an inclined angle theta2 of the line segment OB and the horizontal plane are respectively measured; 2) a rectangular plane coordinate system with the point O acting as the origin of coordinates is established, and the coordinates of point A and the coordinates of point B are substituted into a parabolic model formula y=x2+mx+n of the lead to be measured so that parameters m and n are obtained; and 3) the auxiliary distance measurement device acquires position information of the lead to be measured and forms the position information and the parameters m and n of the parabolic model into a data frame to be wirelessly transmitted to a remote server. According to the method, the modeling process is simplified, the working efficiency is high and the operating risk is low.