The present invention provides an integrally configured flow channel system for application in the basic structure of a paintball gun, which enables increasing speed of vaporization to produce a high working pressure. The structure is solid, and maintains high safety for the operating mechanism. The system mainly includes a gun main body having a long rectangular shape and provided with heat conducting properties, and is longitudinally defined with a bolt. A chamber is defined parallel to the bolt, and a pre-vaporizer is longitudinally defined close to the chamber and the inner surface bordering on the exterior of the gun main body. One end of the pre-vaporizer affords passage to the chamber, and another end is joined to a pressure source through a lead-in port. The pre-vaporizer effectively uses the heat effectively exchanged from the heat stored by the gun main body.