The invention discloses a thermophoretic air purifying device and a thermophoretic air purifying method, and belongs to the technical field of air purification. In a principle of a thermophoretic technology, a stable temperature gradient is artificially created, so that particles in air in a temperature field are enabled to change the motion tracks under the action of a thermophoretic force, are attached to a low-temperature surface and are removed. The thermophoretic air purifying device comprises a shell, a thermophoretic dust tube and a blower, wherein through forced ventilation or thermal pressure ventilation of the blower, air flows through the thermophoretic dust tube and is filtered. Through theoretical calculation, software simulation and real object production test, the thermophoretic air purifying device is proved to have the characteristics of greenness, environment friendliness, no secondary pollution, low resistance, high efficiency of an air filtering device and the like and has a very good filtering effect on fine particles; the average one-pass efficiency of PM 2.5 is nearly 40%, and the highest one-pass efficiency can be as high as 60%; and the thermophoretic air purifying device is simple in structure, and thermophoretic dust tube is convenient to detach for cleaning, so that the maintenance cost is low.