Pulverized coal boiler capable of subcritically combusting lean coal

The invention provides a pulverized coal boiler capable of subcritically combusting lean coal. The pulverized coal boiler comprises a hearth, superheaters, coal economizers and an air preheater. Combustors are arranged in the hearth. The pulverized coal boiler is characterized in that the superheaters include high-temperature superheaters and low-temperature superheaters, the high-temperature superheaters are arranged on the upper side of the hearth, a flue with a vertical shaft is communicated with the upper side of the hearth, two sides of the flue with the vertical shaft are separated from each other, the low-temperature superheaters and the coal economizers are respectively arranged on the two sides of the flue with the vertical shaft, a superheated steam inlet pipeline is arranged below the low-temperature superheaters, an emergency spray attemperator is mounted on the overheated steam inlet pipeline, the flue with the vertical shaft is provided with flue gas temperature regulating barriers which are respectively arranged below the low-temperature superheaters and the coal economizers, and the high-temperature superheaters and the low-temperature superheaters are respectively connected with trim spray attemperators. The pulverized coal boiler has the advantages that the lean coal with the Vdaf (volatile) equal to 14% can be sufficiently combusted in the boiler, so that energy is sufficiently utilized, and the pulverized coal boiler is energy-saving.