The invention provides an automatic spray gun and pipeline cleaning system for a steel pipe UV (ultraviolet) paint spraying line. The automatic spray gun and pipeline cleaning system mainly comprises a spray gun, a pneumatic control switch, a diaphragm pump, a tripod, a paint supplying barrel, a pneumatic tee-joint actuator, a solvent barrel and metal hoses; the automatic spray gun and pipeline cleaning system is characterized in that the pneumatic tee-joint actuator is arranged on the left end of the solvent barrel, and the right end of the pneumatic tee-joint actuator is fixedly connected with the left end of the solvent barrel through one metal hose; the diaphragm pump is arranged on the right end of the paint supplying barrel, and the lower end of the diaphragm pump is fixedly connected with the right end of the paint supplying barrel through the tripod; the paint supplying barrel is arranged on the left end of the pneumatic tee-joint actuator, and the right end of the paint supplying barrel is fixedly connected with the left end of the pneumatic tee-joint actuator through one metal hose; the pneumatic control switch is arranged on the upper end of the diaphragm pump, and the right end of the pneumatic control switch is fixedly connected with the right end of the diaphragm pump through one metal hose. The automatic spray gun and pipeline cleaning system for the steel pipe UV paint spraying line has the advantages that the operation is simple, the process flows such as painting and pipeline cleaning can be finished in short time, so that the production cycle is reduced, and the working efficiency is improved.