Abstract：The Nizhutang molybdenum ore block in the Yuanlingzhai ore district is the largest molybdenum deposit of porphyry type in Jiangxi Province, with very huge ore reserves. The ore bodies in lenticular and bedded forms occur in the internal and external contact zones of the granite, and their thicknesses are from 52 to 456.57 m, with the mean thickness being 227.8 m. The average grade of the ore deposit is 0.067%. In this paper, the authors summarized geological characteristics and genesis of the ore deposit, analyzed the structure and the formation mechanism of the ore deposit, and pointed out that a concealed blasting breccia pipe might exist in the depth. The NE- and NW-trending faults were rock-controlling structures, which controlled the cryptoexplosive breccia and the granite porphyry. The ore-related joints in different directions 50-450 m around the granite porphyry were very well developed, which provided favorable ore storage space for the molybdenum deposit.