Abstract: This study investigated invertase，urease，phosphatase，catalase，dehydrogenase at different soil layers in apple orchard at Weibei arid region，and the relationship between soil enzyme activities and fertility by no-buffer method. A total enzyme activity index（TEI）was established. The results showed that the activities of invertase，urease，phosphatase and dehydrogenase had significant spatial variations and greatly decreased with increasing soil depth；And positively correlated with soil chemical properties significantly except soil catalase and thus can be used to indicate soil fertility. By analyzing the biochemical activities and chemical properties of soil using principal component analysis（PCA），the composite scores of the soil fertility information system with chemical properties and enzyme activities as principal components and TEI had remarkably significant positive correlation with soil chemical properties，TEI is better. These correlations happened similarly at different soil layers. This study indicated that TEI was a better index as an indicator for apple orchard soil fertility than many individual enzymes at Weibei arid region.

Key words: soil, enzyme, apple orchard, enzyme activity, principal component analysis, biological indicator