The invention discloses a gamma-ray flaw detection device for a water-cooled wall tube. The device comprises an exposure tube (1) for emitting a gamma-ray, wherein the gamma-ray flaw detection device further comprises a bracket (2) for fixing the exposure tube (1), the bracket (2) comprises landing legs (3), the foot part of the landing leg (3) is provided with a magnet capable of adsorbing on a water-cooled wall tube screen. Through the adoption of the technical scheme, the bracket can be fixed on the outer surface of the water-cooled wall tube screen so as to fix the exposure tube of the gamma-ray flaw detection device, the exposure tube can be inserted into the outside of a hearth to emit the ray so as to form an image on a film arranged on the outer surface of the water-cooled wall tube screen, therefore, an operation platform and a fixing bracket are unnecessary to be arranged in the hearth, the worker is unnecessary to enter the hearth to work, not only is the working efficiency improved, but also the security is improved.