The invention provides an inner tank of a large high-pressure gas storing and transporting cylinder and a manufacturing method thereof. The inner tank of the gas cylinder is an aluminum alloy inner tank, wherein one end of the inner tank is provided with a seal bottom, and the other end of the inner tank is closed to form a seal head; a cylinder port is of an integrated seamless structure; the inner tank comprises a straight barrel section, the seal bottom and the seal head; the seal bottom and the seal head are correspondingly positioned at two ends of the straight barrel section; the cylinder port is positioned in the seal head; the aluminum alloy inner tank is 5-13m in length; and the nominal outside diameter of the straight barrel section is phi 300-850mm. According to the inner tank of the large high-pressure gas storing and transporting cylinder, a plate blank is used as a raw material and is completely processed by a rotary pressing method; the whole product is free from a jointseal; the preparation processes are simple; the operation is convenient; the energy consumption is small; the pollution is low; the loss of the raw material in the manufacturing process is low. The aluminum alloy inner tank processed by the manufacturing method has the characteristics of being oversize, high in reliability, thin in wall, and light in mass; the material structure is uniform and dense; the overall strength effect is outstanding; the inner tank has the characteristic of being resistant to high pressure and is of an important significance to the manufacturing of oversized high-pressure gas cylinders.