Based on core observation，combined with rock section，cast thin section and scanning electronic microscope，the characteristics and genetic mechanism of volcanic dissolved pore in the northwestern margin of Junggar Basin are studied．It is considered that volcanic dissolved pores developed in this area，including dissolved pore in amygdaloidal filling hole，matrix dissolved pore，phenocrysts and breccia dissolved pore，dissolved pore in filling cracks and intergranular diss0lved pore．The phenocryst in the lava，the plagioclase debris contained in pyroclastic rock and the zeolite formed bv matrix and pozzolanic hydration occurred corrosion partly or completely in an acidic medium，which is the internal cause of dissolved pores。while the acidic solution and the channel for fluid media are the external cause． The interaction intema1 and external causes result in the poor dissolution of effusive facies and strong dissolution of explosive facies．