The invention relates to the technical field of storing and transporting of compressed natural gas and gas filling, and discloses an integrated gas filling semitrailer. A hydraulic system is arranged on a semitrailer, and is provided with a hydraulic cylinder and a pneumatic cylinder, wherein the hydraulic cylinder is connected with a piston rod of the pneumatic cylinder. According to the integrated gas filling semitrailer disclosed by the invention, when a gas cylinder group is under a high-pressure state, high-pressure natural gas can be directly supplied outwards through a complete gas filling device; when the pressure of the gas cylinder group is reduced to a certain value, the hydraulic system compresses the natural gas in the gas cylinder group, and supplies the high-pressure natural gas outwards through the complete gas filling device. The integrated gas filling semitrailer further comprises an internal inflation interface, wherein the internal inflation interface is connected with the pneumatic cylinder of the hydraulic system, so that when the integrated gas filling semitrailer is inflated by another transporting vehicle to be unloaded, the natural gas in the integrated gas filling semitrailer to be unloaded is compressed by the hydraulic pressure system to inflate to the gas cylinder group of the integrated gas filling semitrailer. The integrated gas filling semitrailer disclosed by the invention integrates functions of transporting, gas filling and semitrailer unloading, so that good effects of storing, transporting and filling gas are achieved, and functions of the transporting vehicle are utilized to the maximum extent. The integrated gas filling semitrailer disclosed by the invention has the characteristics of being low in oil consumption and usage cost, safe and convenient to use, and the natural gas is saved.