Based on the atmospheric pressure data from 2001 to 2007 during parallel observation, analyses have been made on the differences between automaticobserved and manualobserved atmospheric pressure data, especially the cause of differences is discussed. The results show that most automaticobserved pressure data are less than manualobserved pressure data. And the higher the sea level elevation is, the more evident the differences are. Because of systematic error in manual pressure formula, the manual pressure data before 2004 are larger than that after 2004. There are obvious daily variation and annual variation in pressure differences. In the higher temperature of period or month, the pressure difference is great always. The statistic results show when the temperature is higher than 30 ℃ or below -30 ℃, the differences between manual and automatic pressure measurements are considerably obvious.