A spray gun system used for SCR-SNCR combined denitration for W flame boilers is disclosed, and belongs to the field of boiler flue gas denitration. The system includes SNCR spray guns and an SCR ammonia spraying grid and also includes a flue gas mixer. The flue gas mixer is disposed in a horizontal flue after an outlet of a coal economizer. The SCR ammonia spraying grid is disposed in a rising flue after the horizontal flue and before an SCR denitration reactor. The SNCR spray guns consist of front-wall spray guns disposed at furnace front wall and a furnace nose spray gun disposed at the furnace nose of a furnace rear wall. The front-wall spray guns are divided into upper and lower layers. The upper-layer front-wall spray gun is disposed above the furnace nose spray gun and the lower-layer front-wall spray gun is disposed below the furnace nose spray gun. According to the technical scheme, reliability, adjustability and safety of the SCR-SNCR combined denitration system are enhanced on the whole.