A high-precision humidity response time measurement has been urgently needed for the fast response humidity sensor in some special situations, for instance, when the quadcopter performs the meteorological observations in the atmospheric boundary layer, the relative humidity changes drastically as it flies into the cloud. So it is essential to gain the accurate response time for these sensors. However, owing to the uncontrollable errors, the conventional methods are difficult to carry out an accurate measurement. Herein, for meeting the requirements above, we designed an accurate measurement method based on a type of switchable chamber and a humidity generator. Among, the chamber was designed through surface molecular dynamics analysis and verified by experiments. It is proved that the switchable chamber with the hydrophobic surface and low water molecule content, combined with the surface to volume ratio S/V =0.2 can achieve the realistic humidity response time of the sensor. For a commercial sensor (SHT20) at 25 ℃, the time corresponding to the 63% and 90% complete responses are 7 s and 49 s measured in this way, which is extraordinarily improved than those traditional ways (51 s and 140 s). As a result, this measurement method could gain the accurate response time for the special situation applications.