The invention discloses a sidewall dominated symmetric combustion low-nitrogen and high efficiency burnout W flame boiler. Furnace arches (arranged burners), staged air and throat over fire air are disposed at the left wall side and right wall side, and exhaust gas burners and wall over fire air are disposed at the front wall side and back wall side. The condition of "symmetric action of the upperhearth asymmetric structure effect on descending pulverized coal air flow", the suppression of a high-depth furnace arch on the upper hearth flue gas flow backward inclination behavior, and the clamping effect of fine pulverized coal flue gas flow from exhaust gas burners and wall over fire air on the ascending W flame backward inclination behavior are utilized to construct the sidewall dominatedsymmetric combustion W flame combustion condition. Symmetric combustion allows intensified stage combustion and reduces local high temperature zone, the fine pulverized coal flue gas flow from exhaust gas burners is organized for re-combustion, and a burnout zone couples with the throat over fire air and the wall over fire air, thus constructing the deep low-nitrogen combustion condition. Symmetric combustion ensures equal burnout on the left and right side, and the fine pulverized coal flue gas flow and wall over fire air reinforce the air flow disturbance and material mixing at the later stage of combustion, thus constructing the high efficiency burnout condition.