Currently, many kinds of plasma jets are used for enhancing the hydrophilicity of polytetrafluoroethylene (PTFE) attributed to the key radical OH by reaction with water. In order to increase the products of OH, the ambient humidity is regulated instead of working gas to avoid the instability of discharge in this paper. And the relationship of hydrophilicity, ambient humidity and OH density coupled with the Ar plasma jet characteristics is investigated. The results show that at water content of 6 mg/L, the electron excitation temperature and the argon metastable reach the peak value. Thus, the OH density reaches maximum of 4 x 10(15)cm(-3), whereas O atoms diminish gradually. Under this condition, more O-polar groups are injected into the surface because of the high production of OH, implying the dominant radical in the surface treatment of PTFE At the same time, the etching effect of the plasma is the strongest. Thus, the smallest contact angle is reduced to 37 degrees. While Oh product at water content of 2.3 mg/L is higher than that of 9.5 mg/L, the contact angle of the former is larger because of the etching effect.