The soil nutrient contents and soil enzyme activities of different soil layers at different seasons in pure and mixed stands of Robinia pseudoacacia and Fraxinus velutina were studied.The results indicate that there were soil nutrient contents and soil enzyme activities differences between different stands,season and soil layers.And soil enzyme activities were remarkably correlated with soil nutrient contents at different seasons.It's also shown that distributions of soil enzyme activities and soil nutrient contents in different soil layers have some regularity,i.e.soil enzyme activity and nutrient content gradually decrease with soil layer deepening.The pH value and salt content in mixed stands were lower than the pure ones,but the growth of tree and soil enzyme activity and soil nutrient content were better than the pure ones.