Abstract: The Radtrak detector used in Gansu investigation was researched and developed. As a high permeable membrane filter for the detector, ²²⁰Rn enters detector with ²²²Rn during exposure period. Gansu cave and traditional dwellings constructed with loam bricks had a high level of ²²⁰Rn, and the measurement results of ²²²Rn were 2-3 times higher than the actual level due to the influence from ²²⁰Rn. The detector was improved by decreasing air exchange rate. Improved Radtrak-R-T detector can effectively distinguish ²²²Rn and ²²⁰Rn, and measure the both simultaneously. According to the sensitivities of the detector to ²²²Rn and ²²⁰Rn as well as the ²²⁰Rn concentration in the room, a correction way for the data of Gansu investigation was established，and the corrected data were compared with the actual measurement results in this area.