The invention discloses a smoke dust detection and purifying method and device applied in a 3D printing sealed cabin. The smoke dust detection and purifying device comprises a gas circulation and purifying system for conducting circulation purifying on gas in the sealed cabin, a smoke dust concentration detection device for detecting the smoke concentration in the sealed cabin, an oxygen detection device for detecting the oxygen content in the sealed cabin and a control device. According to the smoke dust detection and purifying method and device, the gas purity in the sealed cabin is kept by continuously adjusting the rotating speed of a motor of a smoke dust filter; furthermore, the control device detects signals of the smoke dust concentration detection device continuously, gives out corresponding control commands and sends the smoke dust concentration detection signals, the rotating speed level of the motor of the smoke dust filter and the pressure difference signals of a first pressure sensor and a second pressure sensor to a display. By means of the smoke dust detection and purifying method and device, the molding stability and part quality of a 3D metal printing device can be improved greatly, and safety and reliability in the machining process are guaranteed.