Abstract: The calculation principle of grey system GM(2,1) model,exponential curve model and combined model based on optimal weighting method were analyzed.Taking long-term dynamic observation data of groundwater level of a coal mine in Gongyi city of Henan province as samples,three models were used to fit groundwater level respectively.The results show that the average absolute error,square sum error and average absolute percentage error of the combined model are 0.66 7.93 and 0.52 espectively,all of which are lower than those of the exponential curve model and GM(2,1) model.The water level fitted by the weighted combined model is basically consistent with the actual water level.