During radon measurements, radon exhalation monitors are required to be calibrated by a radon exhalation reference device. A reliable correction factor can be obtained only if the effective decay constant used in the calibration matches the one that prevails when the monitor is deployed in the field. Existing reference devices offer limited adjustability of the exhalation rate and no means to tune the effective decay constant. This paper aims to develop a calibration device capable of rapidly and simultaneously adjusting both the radon exhalation rate and the effective decay constant. By investigating the accumulation method for measuring radon exhalation and the mechanism of radon exhalation from the medium surface, this paper explores methods for adjusting these parameters. The radon exhalation rate is adjusted by controlling the activity ratio of radon exhaled from the source to the accumulation chamber, while the effective decay constant is adjusted by actively controlling the leakage rate of the calibration device. The device is divided into two parts：radon exhalation calibration device and a dual-gas-path flow control unit. A dual-gas-path (A/B) flow control scheme is implemented: Path A achieves active leakage via activated carbon, and the flow rates of Paths A and B are adjusted to control the proportion of radon exhaled into the accumulation chamber. Experimental data from dual-parameter synchronous adjustment experiments show that the deviations between the device output values and theoretical values were within two standard deviations in all nine experiments, confirming the feasibility of the method.