The invention discloses a gas boiler smoke discharge device and process. The process includes the following steps of spraying ammonium hydroxide for denitration, redoxing pollutants through low-temperature plasma reaction, spraying dry powder for deacidification, conducting dry-type electrostatic dust removal to remove dust particles and solid salt type particles in smoke, conducting cloth bag dust removal to obtain super-clean smoke, and discharging the super-clean smoke through a chimney. The synergistic, efficient and deep removal of various pollutants (NOX, SOX and dust) in gas boiler smoke of a steel plant can be realized, the discharge of the dust, NOX and SOX can be well controlled, and the super-low discharge of the gas boiler smoke of the steel plant is realized, wherein NOX is smaller than 50 mg/Nm3, SOX is smaller than 35 mg/Nm3, and dust is smaller than 5 mg/Nm3. Meanwhile, the integrated device with the combined optimization design of channel processing, ammonia spraying,plasma reacting, dry powder spraying, electrostatic dust removing and cloth bag dust removing has the advantages of being compact in structure, simple in system process, low in operation cost, small in occupied area and the like.