Objective: To effectively reduce the concentration of poisons in cleanroom, protect the health of workers, realize the optimization and automatic control of the new return air device. And the influence of initial concentration, air volume, temperature and relative humidity of formaldehyde on the purification effect of the new return air device was explored. Methods: The purification effect of the new return air device installed with the activated carbon and the photocatalyst purification net or ordinary activated carbon purification network was tested in a 60 m³ simulated cleanroom. The concentration of formaldehyde was determined by solution absorption-phenol reagent spectrophotometry. Based on the single factor experiment to determine the combination of two purification nets. The effects of air volume, initial formaldehyde concentration, temperature and relative humidity on the purification effect of the new return air device were investigated by orthogonal test. Then, the performance parameters of the return air device to purify formaldehyde were determined. Results: The formaldehyde purification efficiency of the two types of purification nets in the new return air device was higher than that of the ordinary activated carbon purification network (P<0.05) . The combination of activated carbon and photocatalyst purification net has no effect on the formaldehyde purification efficiency of the return air device (P>0.05) . According to the direct analysis and variance analysis, air volume was the most sensitive factor (F value is 18.894, P<0.05) , followed by initial concentration (F value is 16.128, P<0.05) , while temperature and relative humidity have little effect (F value is 0.041 and 0.599, respectively, P>0.05) . LSD analysis showed that there was no significant difference in the purification efficiency of formaldehyde between 475 m³/h and 626 m³/h (P>0.05) . From the perspective of formaldehyde purification efficiency and energy saving, when the air volume is set to 475 m³/h, the new return air device has higher purification efficiency for high concentration of formaldehyde. Conclusion The new return air device consisting of activated carbon and photocatalyst purification net can play a good purification role in cleanroom with different temperatures and different humidity. Its formaldehyde purification efficiency is affected by air volume and initial concentration.