The invention discloses a GDP-mannose transfer protease and a coding gene and applications thereof. A GDP-mannose transfer protease gene DoGMT1 is cloned from dendrobium officinale; the full length ofthe gene is 1745 bp; the nucleotide sequence of the gene is represented by the SEQ ID No. 1; the bases from 203rd site to the 1342nd site encode the GDP-mannose transfer protease DoGMT1, and the nucleotide sequence of GDP-mannose transfer protease is represented by the SEQ ID No. 2. The GDP-mannose transfer protease gene DoGMT1 is one of a nucleotide transport protein family and plays an important role in synthesis of mannan. Through a gene engineering technology, the DoGMT1 gene is overly expressed to promote the synthesis of mannose and polysaccharides; at the same time, the performance ofremoving free radicals is enhanced to improve the salt resistant performance of plants, and the GDP-mannose transfer protease and coding gene thereof have a good application prospect in the breeding of salt resistant plants with a high sugar content.