Research conclusions:The risk assessment is the reasonable way for correcting assessing the risk of the underground water under the condition that the current survey means is limited． The risk assessment of the underground water based on probability analysis presented in this paper is the important development and improvement of the previous assessment of hydrogeologic condition by taking quantitative calculation as the key point． The main factors of the underground water risk include the unstable surrounding rock and change of water quality caused by the volume and way of water bursting，the pressure of the underground water and the change of the underground water as well as the environment change caused by draining the underground water． The obviously local error often happens in the calculation of the hydrogeologic condition because of the uneven watery of the underground water． Conducting the risk assessment can reduce the risk of the big local water bursting caused by the error．