Abstract: The present experiment was conducted in Hulun Lake， Inner Mongolia in June and August， 2014. Soil respiration of 4 kinds of typical grassland （dominant species were Stipa capillata， Leymus chinensis， Phragmites australis and Carex duriuscula） had been measured using LI\|6400 gas exchange system and Li\|6400\|09. It was shown that the diurnal variety of soil respiration of Stipa capillata， Leymus chinensis and Carex duriuscula land was a one peak curve both in June and August， while Phragmites australis land exhibited a steady line. Soil respiration of Stipa capillata， Leymus chinensis， Phragmites australis land in August was higher than that in June. Comparing with the mean value in June， soil respiration of Stipa capillata， Leymus chinensis， Phragmites australis land increased 6281%， 7926%， 23369%， respectively. But， soil respiration of Carex duriuscula land remained the same in June and August.

Key words:  biomass, diurnal variety of soil respiration, soil water content