The sensitivity of thoron monitoring method can be improved largely by applying an electrostatic field in the sampling chamber of thoron dosimeter because more than 90% of the thoron progenies are positively charged at the moment when they generate. The paper introduces a sensitive thoron monitoring method by both using electret to produce electrostatic field in the sampling chamber and using CR-39SSNTD to record α particles emitted from thoron and its progenies. Compared to normal Simultaneous and absorber methods

the new method presents 8 and 33 times sensitivity for thoron monitoring

respectively.