Rare earth element and trace element of molybdenite in the Bangpu Mo (Cu) deposit, Maizhokunggar, Xizang (Tibet), were analyzed by high sensitive inductively Coupled Plasma Mass Spectrometry in this paper. The testing results indicated that rare earth element in molybdenite had the distribution pattern of LREE enrichment and the fractionation in both light rare earth element and heavy rare earth element were obvious. Eu and Ce negative anomalies exist in different degree in the molybdenite. The Eu negative anomaly in molybdenite maybe inherit the characteristics of Eu negative anomaly of the ore forming fluid itself and the Ce negative anomaly reflected that the ore forming fluid were of stronger oxidization property. The high contents of Cu, Pb, Zn and W in the molybdenite revealed that the ore forming fluid was riched in ore forming elements itself. Depletion of high strong field element and the Hf/Sm, Nb/La, Th/La ratios less than 1 suggested that the ore formign fluid was a Cl riched type fluid. Ratios of Y/Ho and Zr/Hf varied in a narrow range indicated that source of the ore forming fluid in the main metallogenic stage was single and stable and had no other fluid injecting.