Abstract: Variations of mean temperature in Beijing city are analyzed in this paper．The results show that the difference of mean daily temperature between city and suburb is the largest on 24 December in 1995 during the last 40 years，and the mean daily ternperature in the city is 4．612 higher than that in the suburb；the difference of temperature between the city and the suburb is the utmoSt in winter season and the mean seasona1 temperature in the city is 1．1l℃ higher than that in the suburb，while the difference is the least in spring season，and the temperature in the city is 0．26℃ higher than that in the suburb；for the inter-annual variability of temperature，the difference of temperature is little from 1961 to 1977，while the difference is great from 1978 to 2000，and the temperature in the city is 0．62℃ higher than that in the suburb，so the heat island effect is reinforced from 1978 to 2000；the difference of temperature is the 1ea st in 1960’s，and the temperature in the city is 0．13℃ higher than that in the suburb，whereas the difference is the maxima1 in 1990’s．and the temperature in the city is 0．7812 higher than that in the suburb；the number of high temperature days(≥3512 )is going up obviously in recent years，but the highest temperature is not changed greatly，and the highest temperature is higher than 3812 only in 1997，1999 and 2000．The mean annual temperature is increa sing apparently during the last 40 yea rs，and it is increa sing by 0．43℃ ／10a in the city and 0．21℃ ／10a in the suburb，an obvious 12 years cycle of mean annual temperature is found．