In mafic—ultramafic intrusions, especially those orebearing intrusions, primitive lateral zoning are common. Traditional gravitational separation theory failed to account for the mechanism to the formation of these occurrences. New patterns of sulfide deposits cannot provide a convincing explanation, too. In the study of magmatic gravitational separation, we found that a gravitational separation accompanied with interference of rapid convection can produce lateral zoning. Based on dynamics analysis, we studied the movement of crystals during the gravitational separation disturbed by rapid convection. Bernoulli Effect was taken into account in our dynamic analysis, which had been generally neglected in previous studies. The paper shows that, a magmatic gravitational separation accompanied with rapid convection can produce a lateral separating effect, causing rapid burial of crystals near the wall. Influenced by lateral separating effect and the cooling near the wall, convection will retreat toward the center of the rising heat flow，and a lateral series of igneous rocks may form，in which the compositions of phases may show progressive changes from wall to center. Since the convection commonly occurred at the early high temperature stage of the magmatic differentiation in a magma chamber, corresponded to the stage of liquid immiscibility of sulfide，the mineralization of Ni—Cu sulfide is usually closely related to the gravitational separation accompanied with interference of convection. Finally, an example is given to explain the formation mechanism of lateral zoning and mineralization. The study result breaks through the traditional knowledge about the gravitational separation, and would be greatly help to deeply understand the evolution of magma and to guide the prospecting for deposits.