Two types of gabbro are exposed in Dachanaban ophiolite in North Qilian Mountains. One is in the lower part of the ophiolite, called gabbroⅠ, whereas the other intruded as dikes into pillow lava with boninite character in the upper part of the ophiolite, called gabbroⅡ. These two types of gabbro show different geochemical characteristics. GabbroⅡis characterized by rich Si, Mg and poor Ti, P, and diabaseⅡand poillow lava associated with gabbroⅡhave features of boninite, suggesting a fore_arc environment. By contrast, gabbroⅠand diabaseⅠis of N-MORB, assuming a back-arc basin setting. Geochemical characteristics of two types of gabbro suggest that their formation environment is an oceanic ridge of low spreading rate.