The natural gas resources in shallow formation are very rich in China. The cost of exploiting gas resources may be reduced markedly by use of geologic drilling rig. It is necessary to research technology and tool equipment for exploiting natural gas resources in shallow formation by geologic drilling rig. The lightweight BOP in this paper is designed for geologic drilling rig. It adopts adjustable top seal,severable ram block and the transmission structure of chain wheels and bearings,therefore it has reasonable design,novel structure, reliable seal and convenient control,and it is also safe to drill.