Abstract: Surface fluxes simulated by both the Simple Biosphere Model(SiB) Version 2 and 3,respectively arc compared to the eddy covariance observations at the sites of Naqu and Anduo in the Tibet Plateau and of Suzhou in the Yangtze Delta region for analyzing the reasons of differences between SiB2/SiB3 and observations, and thus realizing the above areas surface energy budget characteristics.The results show that both SiB2 and SiB3 simulated surface energy fluxes were in very good agreements as compared to field observations.Simulation of the sensible heat fluxes at Naqu and Ando sites using SiB3 is closer to the obscrvations than that using SiB2,but in Suzhou sites,closer using SiB2 than that using SiB3.Simulations of the diurnal variation of the latent heat fluxes using SiB3,arc more consistent with the observations, comparing with Sili2.The correlation cocfficicnts between SiB3 simulated and observed values arc above 0.8 except Suzhou site.SiB2 and SiB3 simulations of the ground heat flux were compared with the observed with the correlation above 0.8.Both SiB2 and SiB3 simulated the net radiation flux reasonably, where the corrclations between simulated and observed values arc generally about 1.0.Compared to SiB2,a soil representation based on the Common Land Model and the prognostic calculation of temperature, moisture and trace gases in the canopy air space have been added in SiB3,which resulted in that SiB3 simulates the latent heat flux and ground heat flux better, but not obvious in simulating the sensible heat flux and net radiation flux over the complex underlying surface.