In the article the obtainment method of average graph of curvatures, observed on terrain surface as a result of underground mining exploitation of hard coal seam, has been presented. Approximation of curvatures measured graph by use of fourth order polynomial divided into a few parts and the least squares method has been done. Average graph of measured subsidence as a first one has been determined. Then average graph of observed curvatures as a second derivative of subsidence approximated values has been obtained. Statistics indicate that proposed method of obtaimnent of average graph of observed curvatures can be alternative for smoothed splines and gives much better results than they. Fourth order of polynomial is enough for determination of average graph of observed curvatures on condition division it into parts.