The invention disclosed a new kind of polypeptide-phosphatidic acid phosphatase 29.81 and the polynucleotide encoding said polypeptide and a process for priducing the polypeptide by DNA recombinant methods. It also disclosed the method of applying the polypeptide for the treatment of various kinds of diseases, such as peripheral nervous demyelination, night blindness, rachitis, fatty liver, bronchial asthma and peptic ulcer. The antagonist of the polypeptide and therapeutic use of the same is also disclosed. In addition, it refers to the use of polynucleotide encoding said phosphatidic acid phosphatase 29.81.