The differences between the extreme ground temperature measured by two different types of temperatures sensors (automatic and manual observation) from 2004 to 2009 at the Mentougou weather station are analyzed. The monthly average differences between the maximum ground temperatures vary from －2.5 ℃ to 2.0 ℃ with obviously seasonal and annual variations, but the difference values have an average rate of 17.5% exceeding the mean value of 2 ℃ and the exceeding ratios decrease year by year. The monthly average differences between the minimum ground temperatures vary from －0.5 ℃ to 2.0 ℃ with obviously seasonal and annual variations, and the difference values have an average exceeding average rate of 3.8%. The influencing factors, such as the intrinsic errors of the platinum resistance thermometers and glass liquid thermometers, soil condition, rainfall, etc. are analyzed. The influences of the different soil environment, installation state, solar radiation intensity, weather conditions, and other external factors are more significant than the errors caused by the instrument itself. The suggestions on reducing human induced errors during ground temperature observation are given, which are helpful to the maintenance and quality improvement of ground temperature observation.