Objective In this study, a novel bio-organic fertilizer was designed by adding sorbitol, which is one of the preferred carbon sources for the functional strain Bacillus amyloliquefaciens SQR9, to the normal bio-organic fertilizer rich in strain SQR9(2×10⁸ CFU·g^–1). The plant growth promotion effect was evaluated. The mechanism for elevation of plant growth promotion effect of the normal bio-organic fertilizer by sorbitol addition was studied.Method The effect of this novel bio-organic fertilizer on cucumber growth, soil biological and chemical properties was evaluated by pot experiments. The effect of sorbitol on plant growth promotion and stimulating IAA (indole-3-acetic acid) production by strain SQR9-gfp was investigated by culturing experiment using Arabidopsis.Result The pot experiment showed that the application of this novel bio-organic fertilizer could promote cucumber growth by increasing the soil nutrient availability and the colonization of strain SQR9-gfp. The addition of sorbitol could promote IAA production by strain SQR9-gfp. Comparing to the wild type Arabidopsis, the plant growth promotion effect of sorbitol addition vanished on the IAA insensitive mutant Arabidopsis pin2.Conclusion These results suggest that the application of this novel bio-organic fertilizer can promote plant growth. The addition of sorbitol can promote IAA production by SQR9-gfp and this is one of the mechanisms through which the novel bio-organic fertilizer boosted plant growth.