The vegetation spatial pattern in drylands, which is dictated by various physical and ecological processes, could be interpreted as an indicator of the ecosystem state. According to the statistical analysis of shrub patch size distribution, we estimated the ecosystem state of desert vegetation in the southeast of the Alxa Plateau. The interactions among shrub populations were shown by point pattern analysis, to illustrate that different species might act as various ingredients in patchiness. Soil properties and roughness of underlying surface were surveyed to support the estimation. Ultimately, the internal mechanism of the differentiation of shrub spatial pattern was discussed. The results show that the truncated power law is the best fitting model for the patch sizes distribution in quadrat 2, while the lognormal distribution is the best for others. Assessment of ecosystem states is verified by the comparation of habitat conditions, which shows that quadrat 2 is better too. The interaction at small scales between shrubs varies with different species, competition dominated relationship is the main reason for the narrowing down of patch size distribution. The positive relationship within species of small patch size, such as Oxytropis aciphylla, is conducive to the formation of diversified patches, whereas species of large patch size with facilitation at small scales, such as Ammopiptanthus mongolicus and Prunus mongolica, give rise to a complex pattern. Sound management should consider to comprise assessment of ecosystem states through shrub spatial patterns, which will provide indications of conservation and restoration of vulnerable vegetation.