In order to study the effect of background pressure on the output performance of HF laser, and to provide referenced data for the “Base-ejecting” HF chemical laser, a series of experiments were conducted with different background pressure for a certain HF laser. From them, the output power and faculae were obtained. The results reveal that, the upper limit of background pressure for lasing is 4 kPa. In addition, the dependence of lasing with diffusional mixing on the cavity pressure is deep, on the other hand, lasing will be generated in high background pressure with injection mixing.