The invention discloses a W-flame boiler with a plurality of groups of overfire air nozzles. The lower part of an upper hearth is provided with a plurality of overfire air nozzle groups. A plurality of overfire air nozzles in each overfire air nozzle group are respectively arranged on a front wall and a rear wall of the upper hearth. Moreover, air blown out from the plurality of overfire air nozzles in each overfire air nozzle group forms an imagined tangent circle at the center of the upper hearth. Three or more over-fire air nozzles are contained in each overfire air nozzle group. The W-flame boiler intensifies the mixing of air in the upper hearth region and unburned pulverized coal, intensifies the smoke filling degree of the upper hearth region, increases the pulverized coal burn-off rate at the later period, reduces a flying ash carbon content and a carbon oxide content, and especially can achieve the aim of reducing the NOx emission load of a boiler on the premises of guaranteeing normal boiler steam parameters and not reducing boiler thermal efficiency under the condition of high deviation of primary air powder of the boiler.