Bacillus amyloliquefaciens is a kind of plant growth promoting rhizobacteria. The response surface experiment and orthogonal experiment were used to optimize the number of trophosome of B. amyloliquefaciens L—H15, and determine the optimal conditions of its solid-state fermentation. In addition, B. amyloliquefaciens L—H15 solid-state fermentation inoculant was applied to cucumber plug seedling in order to verify its actual growth-promoting. The optimized fermentation conditions were identified. The solid matrix was composed of wheat bran and soybean (1∶2.8) with external 20% rice hulls, 0.2% lactose and 0.38% soy peptone. And the ratio of water to matrix was 0.4mL/g, with 46% bottling capacity, and 5% inoculation (108CFU/mL). Under this condition, the number of B. amyloliquefaciens L—H15 trophosome was as high as 1.68×1010CFU/g. L—H15 solid-state fermentation inoculant could remarkably increase the stem diameter, height, leaf area and accumulation of biomass (P<0.05), and significantly enhance the mineral elements contents. The cucumber root activity was increased by 5.86 times than that without L—H15 solid-state fermentation inoculant. Thus, B. amyloliquefaciens L—H15 can effectively stimulate plant growth, and L—H15 solid-state fermentation inoculant had a good prospect in the field of microbial fertilizer. This means that L—H15 is a good candidate of biofertilizer and biological control agent in the future. The application of this kind of solid fermentation inoculant can provide a new way for improving the yield of agricultural products.