Abstract: When stimulating signals with fixed value and varied frequencies are fed to the t extile fiber,the alternating current (AC) resistance fall quickly along with the increase of frequency at first. And after reaching a certain frequencies,the n r ise immediately. The phenomenon is called “AC electric conductivity bathtub eff ect.” Using this effect to design a prompt AC resistance method-oriented test ing system of the textile fiber moisture regain, the dnaio -back on the excessive measuring error and the plate polarization with traditio nal resistance-testing method can be reduced, which can afford the theoret ical proof for designing and developing a new prompt fiber moisture testing device.