Desertification greatly affected the soil respiration and carbon fixation potential in arid and semi-arid area including the Mu Us sandy land of Northern China, and therefore changed the carbon circulation in regional or global scale. In order to reveal the temporal variations of soil respiration and their controlling factors, to understand the effect of desertification on soil respiration rate and the carbon fixation rate in Mu Us sandy land, the main desertification stages in this area were identified in this study as Stipa bungeana communities on fixed dunes (FS), Artemisia ordosica communities on fixed dunes (FA), A. ordosica communities on semi-fixed dunes (SFA) and annual grass communities in active dunes (AL) based on the previous researches. Within each of these communities, we measured the diurnal and monthly dynamics of soil respiration using a LI-8100 Automated Soil CO2 Flux System. In addition, we made field observations of the net primary productivity. The results showed that: Diurnal soil respiration rate varied significantly among different months in FS, FA, and SFA communities, but not for AL communities. For all communities, the highest soil respiration rates were observed in 9:00-10:00, and the lowest at 18:00 in May. However, the highest and the lowest values were observed after 12:00 and at 7:00 from June to September, respectively. In main growing season from May to September, the mean soil respiration rate were 99.79, 88.13, 47.95 and 13.82 mg?m-2?h-1 for FA, FS, SFA and AL communities, respectively. Monthly soil respiration changed significantly for FS, FA and SFA communities, but not for AL communities. Mean soil respiration rate was lowest in May and highest in July. An exponential relationship between monthly soil respiration of FS、FA and SFA communities and monthly temperature was found to be significant. The associated values of Q10 were 5.87, 5.05, 4.02, 0.64, for FS、FA、SFA and AL communities, respectively. Monthly soil respiration was found to be linearly related to monthly soil moisture only for fixed dune communities (FS and FA), but not for SFA and AL communities. A regression model of soil respiration rate against soil temperature and soil water content at 10 cm depth indicted that soil temperature and soil water content accounted for 69% - 87% of the total variance of soil respiration rate in different communities. Linear relationships between monthly soil respiration rate and root biomass were observed for all communities. In main growing season from May to September, both mean root respiration rate and mean soil microorganism respiration rate decreased with worsening desertification. The ratio of root respiration to total respiration were 51.40%, 59.99%, 70.85% and 45.86% for FS, FA, SFA and AL communities, respectively. During main growing season from May to September, net ecosystem productivities were 36.16, 18.56, -11.29 and -22.49 C g/m2 for FS, FA, SFA and AL communities, respectively. The carbon fixation potential of the ecosystem was inversely related to the degree of desertification. Therefore, the facilitation of ecological succession toward S. bungeana or A. ordosica communities in fixed dunes has potential for increasing the potential carbon fixation rate and plant communities growing in Mu Us sandy land.