The Yaji experimental site of Institute of Karst Geology, Chinese Academy of Geology Science, was selected as the study area to discuss the effects of karst physiognomy on soil microbial abundance and enzyme activity. The gene abundances of amoA, as the index of ammonia-oxidizing bacteria(AOB) communities, were determined by real-time quantitative PCR(qPCR), while microbial community population and soil enzymes were analyzed using dilute plate incubation counting and colorimetric methods, respectively. Results show that the enzyme activities and total microbial numbers of soils in saddle back, piedmont slope and karst depression increased while the soil AOB decreased. Moreover, the abundances of AOB communities had a significantly positive correlation with fungi, while it had a significantly negative correlation with sucrase activity.