It is very necessary to improve lateral displacement measurement accuracy for checking the treating effect ,controlling the rate of lateral deformation and guiding the construction of soft ground embankment. Taking the Italy SISGEO inclinometer as an example, and according to the field practice and theory method, this paper expounds the use conventions and test principles of the inclinometer, and illustrates the causes of deflection and twist of the inclinometer casing, then puts forward to corresponding solution measures, and meanwhile, designs an indoor test to verify the feasibility of processing method of the casing deflection.Thereby, it has resolved the error problem due to deflection and twist of the inclinometer casing, and provides a new reference to the use of the digital inclinometer.