The meteorological observations, remote sensing and numerical simulations are used to analyze the Urban Heat Islands(UHI) phenomena over Su-Xi-Chang region on 24 May, 2010. Results show that the UHI intensity has an obvious diurnal variation, which occurs between 0.5℃-1℃ in the early morning and reaches up to 2℃ around midnight. Satellite observations indicate that the UHI intensity was about 5℃-7℃ and because of the strengthening of UHI with increasing of solar radiation, the distribution and intensity of UHI is closely related to the types of the underlying cover and development level. UHI intensity in Suzhou was the strongest, followed by Wuxi. WRF simulations show that higher sensible heat flux and lower latent heat flux in urban areas may enhance the UHI and elevate the boundary layer height. The variation of the thermal and dynamic properties of urban area can significantly alter its surface energy balance, such as turbulent and radiative exchange, thus influence the vertical structure of heat and momentum flux.