The invention belongs to the technical field of radioactive geophysical prospecting in uranium exploration, and specifically discloses a method for finely calibrating a gamma total amount measurement type activated carbon radon measurement instrument. The method specifically comprises the steps of (1), measuring a background value of the radon concentration of an activated carbon bottle; (2), calculating radon concentration calibration coefficients of the activated carbon radon measurement instrument in a first radon concentration range; (3) calculating radon concentration calibration coefficients of the activated carbon radon measurement instrument in a second radon concentration range; and (4) calculating the radon concentration of the activated carbon bottle according to the radon concentration calibration coefficients a and b of the first radon concentration range and the radon concentration calibration coefficients c, d and e of the second radon concentration range, thereby completing calibration for the gamma total amount measurement type activated carbon radon measurement instrument. The method disclosed by the invention can measure the radon concentration in the soil accurately. The radon concentration calibration coefficients of the activated carbon radon measurement instrument can be acquired according to the method, and fine calibration for the gamma total amount measurement type activated carbon radon measurement instrument is realized, so that the radon concentration in the soil can be accurately measured.