Abstract: In order to study the microclimate and provide the basis for changes in grassland ecosystems. Using the June 1-August 31, 2010 open eddy covariance systems and conventional meteorological observation system data, the author analyzed latent heat flux change in Xilinhaote typical steppe grassland and its relationship with environmental factors. The results showed that: June to August overall energy balance closured good closure of 83.9%. Sunny closure was 81.4%, 95.0% cloudy closure, in a range of domestic and foreign similar observation closure of the upper level; latent heat flux. Unimodal quadratic curve, increased gradually after sunrise, around noon reached a peak, and then gradually decreased after sunset stabilized. Sunny and cloudy days latent heat fluxes same trend, but overcast mobility greater amplitude than sunny, and the peak lag sunny; latent heat flux and net radiation, air temperature, surface temperature, surface temperature and the temperature difference, was significantly positively correlated with the relative humidity was significantly negatively correlated with horizontal wind speed correlation was relatively weak. Net radiation which was the biggest factor.