Underground metal mines cavities were serious threats to mineral resources exploitation and the surrounding environment of mines. Useful points′ spatial information about cavity shape could be gotten from 3D laser scanning detection precisely, which had become the main method of cavity accuracy detection. Traditional 3D laser equiangular scanning has its disadvantages of uneven spatial resolution and low efficiency. With the analysis of the irregular characteristics of mined-area, a 3D laser spatial resolution enhancement method was proposed. The formula of calculating the distance between the spiral line and the scanning trajectory was derived. The experimental result of points cloud verifies the efficiency of the new method, which improves the spatial resolution of the 3D laser scanning, and provides a solution for the high accuracy acquisition of 3D shape in the mined-area.