The invention provides a vehicle CNG gas cylinder loading and unloading and carrying device, which mainly comprises three parts, namely a vehicle body, a supporting arm and a loading and unloading hand. The vehicle body is pushed by hands to move forwards and backwards; the supporting arm is designed into a step shape so as to adapt to the narrow space of an automobile trunk and a convex part on an edge of the vehicle; one end of the supporting arm is vertically connected with the vehicle body and can move up and down along the vehicle body, and the other end of the supporting arm mounts and supports the loading and unloading hand; the loading and unloading hand is arranged on a thrust bearing of the supporting arm and is provided with a clamping mechanism so as to grab the gas cylinder; and the loading and unloading hand can rotate on the supporting arm by controlling a rotary operating mechanism. The invention also provides a method for loading and unloading a vehicle CNG gas cylinder. After grabbing the gas cylinder, the loading and unloading hand can take the gas cylinder out of the automobile trunk or put the gas cylinder in the automobile trunk by horizontally advancing and retreating, vertically lifting, rotating and other actions. The vehicle CNG gas cylinder loading and unloading and carrying device has the advantages of solving the problem that the loading, unloadingand carrying of the gas cylinder is labor-consuming, avoiding dangers caused by fall-off of the gas cylinder due to careless manual operation, along with better popularization and application prospect.