Abstract: In order to investigate the effect of compound substrates with different amounts levels of biochar and bacterial fertilizer on the growth of Acer truncatum seedlings, and to obtain the optimal substrate for the seedling cultivation of A. truncatum. Through pot experiment, taking the annual A. truncatum seedling as the test plant object, 16 treatments with 4 doses (0, 10, 20 g/pot, and 30 g/pot) of biochar and bacterial fertilizer were designed for this study. A complete randomized design was adopted to determine physical and chemical properties of different composite substrates and growth, biomass, chlorophyll content, root morphological indicators of A. truncatum. The growth indexes of seedlings were analyzed with principal component analysis, the comprehensive evaluation indexes of seedling growth were screened, and the study on optimal substrate based on the comprehensive evaluation indexes of seedlings. It was found that single application or combined application of biochar and bacterial fertilizer can reduce the bulk density and increase the total porosity of the substrate and reduce the acidity of the substrate. The combined application of biochar and bacterial fertilizer significantly increased the nutrient content of the substrate for nursery. The growth index of A. truncatum seedlings in different composite substrates showed that there were 4 principal components with eigenvalues greater than 1, and the cumulative contribution rate reached 88.048%. The comprehensive evaluation indicators of seedlings obtained from the analysis were total leaf area, fresh stem weight, root surface area and root average diameter. The comprehensive evaluation index of the compound substrate (conventional substrate + 20 g biochar + 30 g bacterial fertilizer) was the highest, followed by the compound substrate (conventional substrate + 30 g biochar + 30 g bacterial fertilizer), which were 0.819 and 0.602, respectively.