The invention belongs to the technical field of rice genetic engineering, and in particular relates to functions and application of a transcription factor gene OsMYB91 in an MYB family relevant to stress-tolerance. The gene has the nucleotide sequence length of 990 bp, and is induced by various stress conditions such as drought simulation, cold, salt, heat shock, and plant hormones including ABA, ACC, NAA, 6-BA, JA, SA and the like; under the natural growing condition, the plant height of an over-expression pant of the gene is obviously lowered than that of a wild plant and an inhibited plant; when a rooting culture medium containing mannitol and ABA is used for treating the seedlings of over-expression, RNAi and wild plants, the over-expression of the gene is discovered to be capable of increasing the resistance to mannitol, and meanwhile, the growth and the germination rate of the transgenic plant are both influenced by an exogenous ABA; measurement of physiological indexes relevant to stress-tolerance of different transgenic plants after the NaCl treatment shows that the gene has the function of reinforcing the resistance of the rice.