Based on the principle of the gas permeation through filter membranes, the paper studied the diffusion ability of three types of membranes which used in solid state nuclear track detectors for radon measuring under four different humidity range. Results show that, the diffusion ability of cellulose acetate membranes and filter papers are apparently stronger than polyethylene membranes, so they are more suitable for radon measuring in solid state nuclear track detectors, however, the effect of humidity is not significant. Finally, we obtain the ...