Soil respiration was measured by using a Li6400-09 soil respiration chamber from May to September 2005 in Stipa krylovii steppe, Inner Mongolia. Environmental variables including air temperature, total radiation, soil temperature and soil water content were also measured during the same period. Our results showed that daily variations of soil respiration could be characterized by a mono-peak pattern. The highest soil respiration rates occurred in between 10:00am and 13:00 pm, and the lowest at about 4:00 am. Seasonal changes of soil respiration can also be described by a mono-peak pattern with the highest (0.14mgCO2m-2s-1) in June and the lowest (0.03mgCO2m-2s-1) in August. While air temperature, soil water content, and total radiation determined both daily and seasonal changes of soil respiration, we found a significant correlation in the seasonal changes that can be modeled as R=0.011W1-0.005W2+6.117×10-5D+0.038 (R2=0.72 P﹤0001), where R is the soil respiration rate, D is the radiation, and W1, W2 are soil water contents in the depth of 0-10, 10-20 respectively. The soil water content at the 0-10 cm depth was found a dominating factor that can account for 51% of the seasonal variation of soil respiration.