Experience of flux measurements over tall canopies has revealed that the eddy flux of sensible plus latent heat is about 30% smaller than the available radiant energy flux. A systematic observation was carried out to investigate the imbalance problem on rice field. The rice field represents a complex system consisting of rice plant, irrigated water and soil. Date obtained in this experiment show that appreciable understimations of sensible and latent heat fluxes are not recognized but understimations of 15 to 23% are counted in the soil heat flux.