Soil enzyme activities and the relationships with soil physical, chemical properties and microbial biomass of eight, typical plots in representative semi-arid areas, were discussed. The results shown that soil enzyme activities were not so high in this region {or shortage o{ moisture and high soil salt content. The trends of soil enzyme activities in the same profile were very similar. Correlation analyses also shown the soil enzymes were affected by respectively soil physical, chemical and biological properties. Especially the organic matter content and microbial biomass have a very closed relationship with many enzymes. The regression equations between soil enzyme activities and chemical properties were obtained by using a stepwise regression method. The principal component analysis reflects that the microbial biomass and the neutral phosphatase have higher coefficient in every major constituents, so these two properties can be considered to be the most important soil biological factors. Finally, the cluster analysis by soil enzyme activities and microbial biomass were conducted. The eight plots can be sorted to different degrees.