The invention relates to the field of backpressure control, and discloses a building method of a unit backpressure model, a control method and system and a unit. The building method comprises the following steps: building a plurality of function relations between unit backpressure and the opening degree of a louver based on the unit backpressure under different boundary conditions and the measuring data of the opening degree of the louver; determining correspondence relation between the opening degree of the louver and the optimal unit backpressure under the condition that the coal consumptionis minimum according to each of the plurality of function relations between the unit backpressure and the opening degree of the louver and based on the relation between the coal consumption under thecorresponding boundary condition and the unit backpressure; and building a three-dimensional model of the unit load, the opening degree of the louver and the optimal unit backpressure based on the correspondence relation between the louver opening degree corresponding to different unit loads under preset weather condition and the optimal unit backpressure. According to the building method, the unit backpressure can be directly controlled through an indirect air cooling system by utilizing the three-dimensional model, so that the power generation coal consumption can be minimized, and the unitrunning economy and the automatic control level of a power plant can be improved.