Abstract: The phenomenon of energy imbalance over heterogeneous surface is very significant. In this paper, a comprehensive field experiment of atmospheric boundary layer (ABL) over the water－land heterogeneous surface was briefly introduced— “Baiyangdian Field Experiment for Heterogeneous Boundary Layer”. The experiment was performed in Baiyangdian area of North China during 8－27 September 2005. Some characteristics of energy budget over this water－land heterogeneous surface are analyzed. The results show that (1) there exists energy imbalance in Baiyangdian region. The sum of sensible heat flux and latent heat flux measured by the Eddy Correlation (EC) method is about 75% of the available energy, while the latent heat flux measured by the EC method is about 70% of that measured by the Bowen Ratio (BR) method, and the sensible heat flux measured by the EC method is about 77% of that by the BR method. (2) The surface latent heat flux and sensible heat flux vary with the net radiation energy. But the latent heat flux is larger than sensible heat flux, which means that the net radiation is consumed for evaporating water from surface. (3) The value of daytime Bowen ratio β is between -0.4 and 0.4, with mean value 0.131, which is influenced greatly by weather condition. The diurnal variation of β is obvious, and the value of β becomes minus when the temperature inversion appears over surface after 1500 LST. (4) The energy balance closure changes diurnally, and increases with the solar altitude.Also, a few remarks and some discussion about the mechanism of energy imbalance over heterogeneous surfaces are given at the end of this paper.