A fixing ring structure for a barrel of a toy gun, wherein a fixing portion is disposed center of a gun body corresponding to a fixing ring, and a position fixing hole is defined in a side of the fixing portion for a gas pipe to embed therein. A though hole and a fixing slot are defined in the fixing ring, and a position fixing ring, a position fixing member, a resilient spring piece and a fixing spring piece are disposed in the through hole. The position fixing ring is disposed center of the fixing ring and the position fixing member of the position fixing ring, wherein the position fixing member is rotated using a special tool to disassemble the barrel disposed between the position fixing ring and the sight device, thereby achieving the objective of rapid disassembly, replacement and assembly of the barrel.