The present application relates to the field of steam boiler, especially to an energy-saving steam boiler, comprising a boiler body and a
flue gas duct installed on the boiler body; a filter plate one and a filter plate two are installed in the
flue gas duct in sequence along the axial direction; the
flue gas discharged by the boiler body passes through the filter plate one and the filter plate two in sequence; the filter aperture of the filter plate one is larger than that of the filter plate two; a spraying ring for spraying water mist is installed on the outer surface of the
flue gas duct; the spraying ring is provided with a liquid inlet
pipe and a plurality of spray heads; the spray heads penetrate into the
flue gas duct; the spraying ring is located between the filter plate one and the filter plate two; the present application realizes the differentiated treatment of different size particle impurities, after the
large particle impurities are filtered and intercepted by the filter plate one, the
small particle impurities are screened out, the space between the filter plate one and the filter plate two is used to spray water mist on the
small particle impurities, the effective
utilization rate of the water mist is improved, and the energy is saved.