Abstract: This paper used four climatic elements:precipitation, evaporation, air humidity, air temperature etc data measured at two meteorological observing stations(an urban site and an open site of the ecologically station) from 1988 to 2002 in Nanjing and the climatologically standard normals in Nanjing(1960—1990).Four elements were analyzer by their yeartoyear trends and the climatic abnormalities (rations)at two stations. The results showed that:(1)the average coincident rate of yeartoyear trend was 90 % or more between the same elements at the two stations.(2)every elements had occurred “abnormality” all (including “extreme” level that it does not exceed 15 % of the “abnormality”).In reality, “abnormality” ratio of a single element in the forest site was more 26 %,but the sum of three and four elements were lees 30 %,in comparison with the urban site. It follows that the urban forest has mitigated function when the climate arises the anomalous fluctuates.