Abstract: Thoron concentration levels were measured in the high background radiation area located in Zhuhai city using solid-state nuclear track detectors. Measurements were carried out quarterly at each location throughout a year. Totally 96 dwellings were selected for the study. Thoron concentration is vary between 3-243Bq/m³, with the geometric mean value being 43Bq/m³. The dwellings with tile configuration and earth floor have highest thoron concentration. Existence of high thorium content in the soil leads the high thoron values. Increasing ventilation rate inside the dwellings enhances inversion currents and lifts more thoron from the ground, which make the higher concentration of thoron in dwellings.