Carboniferous volcanic rocks in the oil and gas reservoirs are almost all gathered in fault traps in Santanghu basin， reflects the faults of the volcanic gas reservoir has a strong sealing ability．Study suggests santanghu basin and Carboniferous volcanic rocks in the fault basin with two vertical and lateral seal．Vertical sealing depends primarily on the fracture filling line for pressure，but the main row size for pressure and filling ingredients and filling level. In volcanic rocks of volcanic rock fracture filling is nothing more than their own broken rock debris and mud， mudstone filling under certain conditions with good sealing，the simple volcanic debris filling their general non-closed. However，since the Carboniferous volcanic rocks in effect by the hydrocarbon base fluid, explain the formation of alkali＂on the silicon under the base＂of the result will SiO2 layers in the local volcanic debris cemented itself broken up, the formation of vertical closure．Therefore, the volcanic rocks in the clay filled fault exists and vertical sealing cement two kinds of mechanism of SiO2．In fault corresponding volcanic reservoir，oil and gas are usually present＂the shift＂phenomenon，this is a manifestation of lateral seal．Looking from causes the difference infiltration factor，volcanic rock in the presence of lateral seal butt，shale smear and cementation closed three kinds of mechanism．Each mechanism under different geological conditions in the oil and gas accumulation on the role of volcanic rock．