Abstract: The microclimatic observation was conducted over the rooftop and the ground in urban and suburban areas of Kunming City of P.R.China. The main results obtained in this paper are summarized as follows: 1. The wind speed over the rooftop and the ground in the suburban are larger than in the urban area, and in daytime the differences are markable. 2. The air temperatures over the ground in the urban area are higher than in the suburban area at majority times. At night the differences are larger, the maximum is 2.7℃(at 7:00). Because the influences of different factors, in the same day the urban heat island appear, the urban cold island may appear too. 3. The variation of the urban heat island in rooftop is different from that on the ground. The maximum appears 14:00 of fine day. The mechanism responsible for urban heat island is the differences in the rooftop and on the ground. 4. The air temperatures over the rooftop are larger than over the ground. That expressed that the rooftop is the second thermodynamic surface in the urban area. There exist differences of vertical variations of the air temperature in the urban and suburban areas. 5. Because the position and the character of surface and the sky condition are different over the rooftop and on the ground in the urban and the suburban areas, the characteristics of the urban climate are different.