Abstract: The comparison testing observations of water level earth tide and water surface fluctua-tion have been made under the condition of three different well apertures at Mishan well in Heilongjiang Province.After the elimination of water level tendency variation and barometric effect, the earth tide coefficient(Bg) of water level showed an increase tendency with the de-crease of well apertures and the amplification rate of water level fluctuation also showed an increase tendency with the decrease of well apertures.Therefore, the authors think that to re-duce the diameter of upper water level variational section maybe can raise the earthquake-response ability of observed wells.