In order to study the effect and function of fertilization on soil biological characteristics in Larix principis-rupprechtii plantations, we chose 20 years old Larix principis-rupprechtii plantation in the Nantan nursery garden of Taibai county in Shaanxi province as the experimental sites, and set up different fertilization treatments, and studied the effect of different fertilization treatments on soil enzyme activity (sucrase, urease, phosphatase, catalase) and number of microorganisms (bacteria, fungi, actinomyces) by combining field sampling and indoor analysis. The result showed that all fertilization treatments enhanced soil activities of catalase, phosphatase, urease and sucrase. Nitrogen and phosphorus combined treatment had the greatest effect on enzyme activity in May and July. All fertilization treatments enhanced soil actinomycetes number, nitrogen and phosphorus combined application had the most obvious effect. Applying only nitrogen reduced the number of bacteria, and 75 kg/hm² nitrogen and 75 kg/hm² phosphorus treatment reduced the number of soil fungi. Soil enzyme activity and soil microbial quantity increased first and then decreased with the promotion of month. The result of this study showed that applying fertilizer could improve soil biological characteristics and effectively alleviate the fertility decline of 20 years old Larix principis-rupprechtii plantation