The quality assessment (QA) method which includes the steady state test of the CO2 flux, sensible/latent heat flux and integral turbulence characteristic test of the vertical velocity was used to analyze the turbulence flux data observed by eddy covariance at Xilinhot, 2009. The main results are as follows. The data are good on the whole and there are 80% data well assessed by the QA method. The good data size in daytime is more than in nighttime and in summer is more than in winter. From the comparative analysis, the pre processing work can eliminate most bad data. Furthermore, the quality of the data assessed by the QA method will be obviously improved. Using these good data to analyze the energy balance, the closure of the local energy balance has increased by more than 2%.