Abstract: To search for the correlation between soil enzyme activities and soil fertility under the long-term fertilization conditions, enzyme and soil nutrien t through a 12-year fertilization experiment in fluvo-aquic soil were detected an d analyzed. The results were as follows: Long-term application of NPK fertilize r s combined with organic manure could significantly increase the contents of orga nic matter, both of total N, P and available N, P, K . Similarly, the soil phosp hatase, urease and invertase activities were increased. Returning of corn straw into field was helpful to increase soil invertase activity mainly. Farm yard man ure laid particular emphasis on the augment of soil phosphatase, urease activiti es. Crop rotation has more effective than that of continuous cropping to increas e soil fertility. The correlation between soil enzyme activity and soil nutrient content was significant. Positive correlation was found between the activities of phosphatase, urease and invertase and the contents of organic matter, total P and available P. In addition, the positive correlation of phosphatase activity with the contents of available K and alkalified N, urease activity with the cont ent of available K, invertase activity with the content of alkalified N, were si gnificant. Long-term fertilization couldn't increase the soil hydrogen peroxida s e activity. The correlation between hydrogen peroxidase and soil nutrient conten t was not obvious.