The accurate evaluation of karst development situation is hard to be given in the investigation and design phases for karst tunnel, so it’s necessary to establish dynamic classification method for karst tunnel during construction. This paper got the quantitative assessment method of surrounding rock dynamic classification for karst tunnel through the comprehensive revision of basic quality indicator of rock. And the method is applied to the karst surrounding rock dynamic classification of the Xianrendong tunnel, which made the surrounding rock classification, closed to the actual conditions and ensured the safety and rationality of the construction.