On 12 May, 2008, a great sized earthquake of magnitude Ms= 8.0 occurred in Wenchuan County, Sichuan Province, southwest China. Many residents established a great of tents on all urban public and residential greenbelt for searching safe sites. However, there are few reports about the effect of these activities on soil and vegetation. We determined soil CO2 efflux and relative environmental factors (i.e., bulk density, porosity, air temperature and humidity, and microbial biomass)in the field camping sites of different established time and trample area. Soil CO2 efflux was significantly affected by field camping and trample. Soil CO2 efflux was significantly lower in the different field camping sites and trample area than in CK treatment. Soil CO2 efflux decreased firstly (after about 10 days), then increased little (after about 20 days) and again decreased (after 25 days) following field carmping time increasing. Soil compaction and shade was two main processes controlling soil CO2 efflux in field camping sites. In early periods, shade that caused root respiration decline was main process. With the increase of extent of compaction, soil physical properties were main factors. In trample area, soil compaction was main process that affected soil CO2 efflux. So, scarification that improved soil physical properties was the first work to restore degraded urban grassland after 5.12 Wenchuan great earthquake.