The reduction coefficient of water evaporation between evaporation tank and different kinds of evaporators and its varying rules are analyzed, based on the multi-year evaporative data in Nansihu Lake evaporation station in Shandong Province.The installments, the structure and the making-material of the evaporators, which may affect the reduction coefficient, are also studied.Finally, we find out that the coefficient between the evaporation tank and different types of evaporators useful to water resources analysis and evaluation as well as engineering hydrology calculation and design.