Abstract: A calibration device for a radon exhalation rate measuring instrument and radon exhalation rate control method thereof is provided, and relates to the field of radon exhalation rate measurement. The device includes a diffusive solid radon source, a solid radon source containing chamber, a radon accumulation chamber, a diffusion medium, an air pressure balancing device, a support frame and a fixture; a circular cone opening at a bottom of the radon accumulation chamber is connected with the solid radon source containing chamber, a top of the radon accumulation chamber is sealed by the diffusion medium, the diffusion medium includes a plasterboard and a high-density wood board, the high-density wood board is on the plasterboard, the air pressure balancing device is connected with the radon accumulation chamber, and configured to maintain dynamic balance between the radon accumulation chamber and ambient atmospheric pressure.