The invention relates to a soot blowing system and method used for a boiler horizontal flue. The soot blowing system and method are mainly used in a coal-fired boiler. The soot deposition phenomenon is serious at the furnace arch of the coal-fired boiler horizontal flue, and no effective solution exists at present. The soot blowing system comprises a compressed air main pipe and a plurality of soot blowing units. Each soot blowing unit comprises a compressed air branch pipe, a manual brake valve, an electromagnetic valve, a pressure gauge, a plurality of air caps and a plurality of anti-abrasion tiles. The soot blowing system is characterized in that the compressed air branch pipes are connected with the compressed air main pipe; the manual brake valves, the electromagnetic valves and the pressure gauges are all installed on the compressed air branch pipes so that each compressed air branch pipe can achieve the function of blowing soot alone; the manual brake valves, the electromagnetic valves and the pressure gauges are all located outside the boiler; the air caps are directly fixed to two adjacent fins of two adjacent water cooling wall pipes in the boiler; the air caps and the compressed air branch pipes are connected; and the anti-abrasion tiles are installed on the water cooling wall pipes in a sleeving mode. According to the soot blowing system and method used for the boiler horizontal flue, adjusting is convenient, and the soot blowing effect is good.