The characteristics of grass surface heat flux under different weather conditions in autumn and in winter have been analyzed based on data measured with Eddy Covariance method at Longmen long-term observation station during the period of September 2009 to January 2010. The results indicate that there is a large monthly variation in the energy balance under different weather conditions. The daily variation shows a typical single-peak circle on clear days (except long-wave radiation) and a double-peak or more-peak curve on cloudy and rainy days. The value of upward long-wave radiance is slightly larger than that of downward long-wave radiance. The difference of values between these two kinds of radiance is the smallest on rainy days and increases on cloudy and clear days. The upward long-wave radiation

the downward long-wave radiation

the solar radiation

the net radiation and the upward shortwave radiation show the descending contribution to the radiation balance. Each component of surface energy flux shows obvious synoptic conditions and seasonal and monthly variations. The latent heat flux is larger in autumn than in winter

whereas the sensible heat flux is opposite. The latent heat flux and the sensible heat flux are both reduced on cloudy and rainy days. A negative watervapor transfer exists at night. The soil heat flux is negative on rainy days and the daily average value of rainy days is higher than that of clear and cloudy days. The soil temperature of surface and shallow-layer (5cm) presents accurate sine curve changes regardless of clear days and cloudy days. The soil temperature active layer is in the 10cm scope. The time when the soil temperature reaches the maximum (minimum) is delayed with increasing soil depth. There is no diurnal variation below 10cm depth. The soil temperature of surface and shallow-layer decreases with time on rainy days. The soil temperature of each layer is higher on clear days than that on cloudy days and higher in autumn than in winter.