The invention provides a fortunella.crassifolia FcWRKY70 gene and an application of the gene in improving the drought tolerance of plants. A multi-adversity-induced WRKY transcription factor FcWRKY70 is obtained from fortunella.crassifolia by isolation and cloning and by the applicant and has the sequence as shown in SEQ ID NO.1 and the coding protein as shown in SEQ ID NO.2; the gene is introduced into tobaccos, lemons and fortunella.crassifolia by the applicant respectively, so that the drought tolerance of the obtained over-expression transgenic plants is remarkably improved and the drought tolerance of intervened transgenic plants is remarkably weakened. According to the gene and the application thereof, a new gene resource is provided for plant anti-abiotic-stress molecular design breeding as well as a new genetic resource for a green water-saving agriculture, and the development and utilization of the genetic resource are beneficial to reducing the agricultural production cost and promoting high-efficiency development of the agricultural industry.