The regularity of radon exhalation is affected by the weather and the ventilation in the over-broken granite tunnel. Based on the calculation model of radon exhalation in tunnel， some experiments have been carried out to analyze the variation of the radon exhalation in natural ventilation， blowing and exhaust conditions separately. The result showed that there is a linear relation between the radon exhalation and the natural ventilation， the temperature outside the tunnel also works as the same. It also shows that in the same condition of the tunnel's air flux and the outside temperature，the radon exhalation in exhaust case is 63% higher than the blowing case. When the temperature outside is high works in tunnel should avoid， and the blowing ventilation could be an effective way for reduction of radon concentration.