The invention discloses a flue gas emission pollutant control process device for a coal-fired boiler in a power plant and a control method. The device comprises three parts, including a pulverized coal gasification system, a flue gas heat recovery system connected with the pulverized coal gasification system, and a purification system connected with the flue gas heat recovery system; the pulverized coal gasification system is used for producing fuel gas with low calorific value, SOX and NOX in flue gas are removed under the action of synthesis gas at the rear of the boiler in the flue gas heat recovery system, and heavy metal and halogen in the flue gas are removed through the purification system. The flue gas emission pollutant control process device has the advantages of simple and available raw materials, no secondary pollution, high pollutant removal efficiency, and no influence of smoke components on pollutant removal efficiency, and can realize efficient and synchronous removal of NOX, SOX, halogen, mercury, lead, chromium, arsenic and other flue gas pollutants.