The invention relates to a gun, in particular to a gun barrel capable of improving firing precision of the gun. Vertical small holes are formed above the axial line at the front part of the gun barrel, so that the defect of muzzle jump during the design is overcome. The vertical small holes are formed above the axial line at the front end of the gun barrel. A conical groove is formed on the inner wall of the gun barrel and communicated with the bottom ends of the small holes, and the upper end of each small hole is flared for forming a V-shaped port section. The number of the vertical small holes is two in a best way. The distance from the small hole at the most front end to a muzzle is within 5mm, and the distance from the other small hole to the small hole at the most front end is also within 5mm. The gun barrel disclosed by the invention can enable the gun barrel to produce downward motion trend force because reaction force formed by injection of ultra-high pressure gas flow acts above the gun barrel, offset muzzle jump force and greatly improve the target firing precision.