Integrated and flexible double membrane gas tank from the inside dual-mode two layers, between the intima and the inside membrane for storage of biogas, hemishpere, 1/3 sphere, and assembling tank or tank welding, cement tank connection, form a whole project. In the inner and outer membrane interlayer, the design pressure of the inner gas of the membrane is kept by using the constant pressure of the inlet air of the equipment. Gas holder has the advantages of simple construction, easy installation and maintenance. The whole system is easy to manage and easy to operate.