In desertified grasslands of the arid Urad Rear Banner of the Inner Mongolia and the semi-arid Yanchi of Ningxia, the Caragana korshinskii shrub microhabitats beneath shrub canopies and in the open spaces were setup as study sites. The litter of Reaumuria soongorica was used as the research object. Two sizes of mesh (30-mesh, and 250-mesh) for litter bags were used to explore the role of soil microarthropods on litter decomposition of Reaumuria soongorica. The objective of present study was to probe into the mass loss of the litter and the contribution of soil microarthropod community in the shrub microhabitats. The results showed that:(1) there was no significant difference in decomposition constant K of litter between shrub canopy and open spaces; the presence or absence of microarthropods had little effect on K. (2) At decomposition stage of 12 months, there was significantly lower mass remaining rate of the litter in open spaces than beneath shrub canopy without the presence of microarthropods, but there was no significant difference between shrub canopy and open spaces in the case of microarthropods presence. At decomposition stage of 44 months, the mass remaining rate of litter was significantly higher in open spaces than beneath shrub canopy only in arid regions without the participation of microarthropods; however, there was no significant difference between both shrub microhabitats with microarthropod presence in both arid and semi-arid regions. (3) The contribution rate of microarthropods to the mass loss of litter showed a unimodal type during decomposition process, with a single peak at 24 months. At decomposition stage of 12 months, there was significantly lower contribution rate of microarthropods to the decomposition of litter in open spaces than beneath shrub canopy only in semi-arid region. At decomposition stage of 44 months, the contribution rate of microarthropods to the decomposition of litter was significantly higher in open spaces than beneath shrub canopy only in arid region. (4) In the semi-arid region, the contribution rate of microarthropods to litter mass loss was closely correlated to the group richness of microarthropod, soil sand content, soil total carbon, and water content. In the arid region, however, the contribution rate of microarthropods to the mass loss of litter was closely correlated to soil pH, soil sand, soil C/N, and clay and silt content. In conclusion, the overall litter decomposition in shrub microhabitats in arid and semi-arid regions was little affected by the role of microarthropods. However, at certain decomposition stages, the difference in mass loss of the litter between shrub microhabitats was affected remarkably by the role of microarthropods. There was a law of weak (12 months)-strong (24 months)-weak (44 months) role of microarthropods on litter decomposition that was regulated by the climatic factors.