The invention relates to a rhizopus oligorrhizae fungus and its application in the production of Pu'er tea, which belongs to the field of biological technology. Rhizopus arrhizus of the present invention is obtained after traditional preliminary screening, re-screening, natural culture medium cultivation, and rhizopus purification and cultivation procedures by producing bacterial strains and auxiliary materials, and the producing bacterial strain is Rhizopus arrhizus (Rhizopus arrhizus) Prhi501, preserved In the General Microbiology Center of the China Microbiological Culture Collection Management Committee, the address of the preservation unit is: No. 13, Beiyi Yiyi, Zhongguancun, Haidian District, Beijing, the preservation date: March 1, 2007, and the preservation number: CGMCC No.1963. The Rhizopus oligorrhizae fungus can improve the quality of Pu'er tea, and can be applied in the production process of Pu'er tea. The present invention has the advantages that: the rhizopus abacifolia fungus is used in the large-scale production process of Pu'er tea in the proportion of 0.1-0.8% by weight, and the tea polyphenols and theabrownin in the Pu'er tea can be controlled at an appropriate ratio. It achieves the effect of improving quality, shortens the processing time, and plays an important role in stabilizing and improving the quality of Pu'er tea.