The invention discloses application of protein AtbHLH122 of Arabidopsis thaliana and a coding gene of the protein AtbHLH122 for regulating and controlling the stress tolerance of plants. The amino acid sequence of the protein is shown in a sequence 1 of a sequence table and can be used for regulating and controlling the stress tolerance of the plants, or substances and methods, capable of adjusting the expression level of the protein shown in the sequence 1 of the sequence table, can be used for regulating and controlling the stress tolerance of the plants. Shown by experiments, after the coding gene of the protein AtbHLH122, which is shown in a sequence 2 of the sequence table, is over-expressed in Arabidopsis thaliana, a transgenic Arabidopsis thaliana plant is obtained, the survival rate after drought treatment, the germination rate and leafy rate after 140mM NaCl treatment and the root length after 250mM mannitol treatment of the transgenic Arabidopsis thaliana plant are remarkably lower than those of the wild plants, and furthermore, after the treatments, gene AtbHLH122 knockout mutants are less than those of the wild plants; and thus, the protein AtbHLH122 shown in the sequence 1 of the sequence table has the function of regulating and controlling the stress tolerance of the plants and has an important significance on the aspects of stress tolerance research and breeding of the plants.