On the basis of the hydrogeological characteristics of hot mineral springs in Xiaotangshan area,Beijing,authors engaged in the experiments of water-rock reaction using dolomite (90%)and granite (10%)as starting materials and quadratic distilled water as reactive solution, which were put into Ti-high pressure vessels under 50-200℃and (200一500)×lO5Pa. The results of experiment showed that the quantites of ions and oxides for K+, Na+, Ca2+, Mg2+,Al3+，HCO3-,N03-，F-，C1-，SO42-,∑Fe and Si02 extracted from the rocks into the solution cange with the variations of rock compositions, temperatures,pressures, pH values of water, grain sizes of rock, redox state, and numbers of time for water cycle etc. These laws brought to light the mechanism of the main elemental change in the formation of hot mineral springs in Xiaotangshan area. Authors provided the oretical evidences for opening up hot fields and man-made hot springs.