For a passive radon detector of Solid State Nuclear Track Detector (SSNTD), the measurement results can be affected under an environment of high humidity. In order to correct this kind of measurement errors, experiments in normal radon laboratory were performed. The track films were etched in 6.25 mol/L NaOH solution at 70°C for 12 h, and rinsed with water for 6 h. The experiment results show that calibration factor of the SSNTD decreased with increasing humidity, because of increased stopping power of the moisture-absorbed film surface to α particles. Therefore, the calibration factor K should be corrected from the calculated result.