The Chinese Tianshan orogenic belt is located in the southern part of the Central Asian Orogenic Belt (CAOB) in north Xinjiang, NW China. The Erhongwa mafic ultramafic intrusion is at the western part of the Huangshan mafic ultramafic rock belt which is located at the eastern part of the north Tianshan orogenic belt, can be divided into two small intrusions which named north and south intrusion, the area in the surface is 1 42km 2 and 6 25km 2, respectively. The Erhongwa intrusion is a multiple intrusion and composed of two intrusive rocks units, the first period have plagioclase bearing lherzolite and olivine gabbro, and the second period which is composed of gabbronorite and gabbroic rocks. Olivine crystals enclosed in large clinopyroxene and plagioclase crystals from the plagioclase bearing lherzolite and olivine gabbro have Fo contents between 80 9~89 7 mole %, and the contents of Ni in the olivine crystals between 102 19~4319 66 ppm, which decrease rapidly with Fo contents indicating sulfide segregation from magma during olivine crystallization. Numerical modeling using bulk sulfide compositions and constraints from olivine liquid relation reveals that the parental magma of the Erhongwa mafic ultramafic intrusion was a high MgO theolitic magma containing 10 3 wt % MgO and 10 8 wt % FeO. The estimated MgO content in the primitive magma is up to 15 73 wt %. At 2 kb total pressure and the oxidation state of QFM 1, olivine start to crystallize at 1368℃ according the MELTS program, the sulfide segregation and olivine fractional crystallization occurred almost at the same time during the magma evolution, and the sulfide: olivine is 1:50~100. The petrology and mineralogy characteristics and the modeling calculation results suggest that the Erhongwa intrusion have the basic conditions for form the Ni Cu deposit, but the previous sulfide segregation in a staging chamber lead to the depletion of the ore forming elements (e g , Ni, Cu) in the parental magma. We need to find the sulfide melt which is formed by the previous sulfide segregation in the staging chamber and the favourable areas of metallogenic enrichment.