Abstract: The microbehaviour of groundwater level in a borehole is engendered by stress changes in the earth crust.These stresses are commonly produced by the earth tide,atmospheric pressure,loading of the precipitation,loading of the surface water,and activity of a fault etc..The formative process of the microbehaviour is as follows:(1)The earth stress is changed;(2)The stress change causes the deformation of an aquifer,and the deformation leads to generate the change in a pore pressure;(3)The change of pore pressure causes a water-flow between the aquifer and the borehole;(4)The flow results in the fluctuation of water level in the borehole.This paper discusses the key links in the above processes from the viewpoint of rock mechanics,soil mechanics and groundwater dynamics.Moreover,it suggests some principles to choose or evaluate a borehole for seismological observation.