Abstract: Surface energy imbalance is a difficulty in the study on land surface interaction. A series of experiments related to surface energy imbalance have been conducted in different climate zones and underlying surfaces in the world. Over the past two decades, some systematic progresses on this issue have been made. This paper summarizes the research achievements of surface energy balance in land surface process experiments conducted over different underlying surfaces, introduces the statistical methods to characterize surface energy imbalance, and discusses the possible causes resulting in energy imbalance. Heat storage in upper soil layer and energy storage due to plant photosynthesis and temperature variation of canopy and air has an effect on surface energy balance. Vertical sensible advection is also discussed as a cause resulting in surface energy imbalance. Because of footprint differences of energy components, heterogeneous surface has an impact on representation of measurements, and it also induces local circulations and largescale eddy. Together with the nighttime inadequate turbulent mixing, the inconsistent atmospheric status makes some troubles to the flux measurements. After data quality control is processed strictly, three schemes are put forward to solve the energy imbalance, heat flux advection correction for singlepoint EC system, spatial averaging of flux observations for multipoint one and the replacement of EC system by LAS with  larger measurement footprint. It is suggested that the nighttime EC latent heat flux be substituted by the PenmanMonteith modeled flux in cases of insufficient turbulent mixing. A simple discussion is made by a comparison between the EC water vapor flux and the actual surface evaporation observed by the weighing evaporation instrument and the weighing evaporation instrument as a possible test method, and it is proposed to calculate surface latent heat flux.

Key words: land surface, energy balance, earthatmosphere system, underlying surface, circulation, heat flux