Abstract: Surface crack is a kind of mining-induced damage. Due to research means and methods, there is few study on the quantitative calculation of the width of mining-induced surface cracks. In this article, based on the measured data, the surface crack width indeced by mining is deduced according to the geometry theory. Compared with the measured data, it shows that the calculated results coincide with the measured data, which provides the judgment method for the coal mining area land reclamation engineering and land damage degree.