Abstract: A measurement method of thoron exhalation rate is developed based on the characteristic of thorium C' which emits a α particle with higher energy than those of α particles released from radon and radon progenies. The principles of discriminating radon and realizing thoron exhalation rate measurement on the material surface with absorber, the passive and integrated thoron exhalation rate monitor studied, and its calibration coefficent determination method are introduced. The effectiveness of mitigating thoron exhalation rate of wall surface by depresurization inside wall and thoron exhalation rates on some materials surfaces were measured by using the studied monitors. The calibration coefficient of the studied monitor is R=0.246 cm-2·(kBq·m-3·h)-1, The lower limit of detection is LLD=18.4 mBq·m-2·s-1 when the sampling period is 7 days and the standard deviation of background track densities of the adopted CR39 SSNTD is sT=1.6 cm-2.