There are many previous researches about how the environment conditions affect on the efficiency of the fibrous filter. But most of these researches are focus on the air face velocity and the loading particles size. But in fact, air relative humidity is also a very important environment condition factor affect on the filter efficiency. The way of how the filter efficiency influenced by air relative humidity could be generalized as the follow 2 mechanisms The first is the electrostatic. There is static electricity on the filter surface, but under different conditions, the surface potential of the static electricity was different. The different electrostatic attractions lead different efficiency. The second is the air relative humidity affect on the particle size. The nucleation and condensation always happen in the filtration processing. The air relative humidity may affect on the nucleation and condensation rate of aerosol. So the air relative humidity could indirect influence the filter efficiency. The deposition mechanisms of fibrous filter already became a theoretical system, but in the calculation there is no the factor of the air relative humidity. So if the correction factor of air relative humidity could be added in the deposition mechanisms, then the theoretical system of the fibrous filter will be more accurate. From the test results we could see that the variation tendency of the filter surface potential, and how the RH affect the surface potential.