The Niujuanzi ophiolite determined by previous studies is regarded as an important evidence for the division of Beishan tectonic units in Gansu Province, NW China, but the authenticity of its petrological properties has not been effectively verified. Detail field investigations with 1∶50 000 scale have allowed us to revisit the rock association, contact relationship and field occurrence. Meanwhile, geochemistry of Gabbro are also analyzed and discussed. The results show that the rock assemblages developed in the area may be the products of plutonism rather than a typical ophiolite. Evidences are listed as follows: ① The pseudo- sequence of ophiolite rock association is seriously missing in Niujuanzi tectonic belt. ② Volcanic lava developed with few and sparse in local section of the belt. ③ Ultrabasic rock including abyssal peridotites are missing. ④ There is no any characteristics of mélange zone. ⑤ There is no material components that resemble those style of ' rock block and matrix ' of a typical suture zone. ⑥ There is no record of deep- sea deposition such as radiolarian bedded chert. ⑦ On the contrary, gabbro has obvious geochemical characteristics of crust—mantle mixed source, which is quite different from the trace element characteristics of N- MORB and OIB. Thus, the so- called Niujuanzi ophiolite is a suite of complex pluton mainly including gabbro intruded into the surrounding rocks, the Misjudgment of the tectonic nature of which could attribute to the relatively low and gentle topography and serious coverage of loose deposits in the Beishan Mountain.