Pot experiments were carried out to investigate effect of application of amino acid fertilizer (AAF) on biological properties of cucumber plants (Cucumis sativus) and soil microorganism under continuous mono-cropping.Results show that application of AAF increased chlorophyll content,leaf area,photosynthesis rate,and dry weight of the cucumber plants.Moreover,after the application of AAF with high-quality carbon,the number of actinomycetes was increased by 1.57～2.18 folds,fungi by 2.22～8.43 folds,while the number of Fusarium oxysporum,a witling disease causing fungi,was significantly decreased.The ratio of Fungi/Bacteria was significantly increased while the ratio of F.oxy.to fungi was significantly decreased.The rate of protection of fusarium wilt was more than 80%.The results suggested that AAF application could significantly promote the growth of cucumber plants,stimulate microbial activities in the soils,and alleviate the adverse effect of continuous mono-cropping of ucumber.