Abstract: In order to know the gas emission of Yangshan tunnel during construction so as to determine the its gas level, the maximum volumes of gas emission from coal seam and the natural gas from oil reservoir were predicted using different-source forecast method and drilling flow method, based on site testing of the basic parameters and analysis on occurrence law of gas in coal strata and natural gas in oil reservoir. Meanwhile, a mathematical model of gas emission prediction of this type tunnel was established. The research results show that the coal seam through which the tunnel passes is located at a nitrogen band of gas weathering zone without dangers of coal burst and gas burst,and the maximum volume of gas emission from the coal seam is 0.037 m3/min; the maximum volume of natural gas from oil reservoir is 0.234 m3/min. So the maximum total volume of two kinds of gas source emission is 0.271 m3/min,much less than 0.5 m3/min, which means the tunnel could be determined as the low gas tunnel. The mathematical gas emission prediction model will provide a new method and approach for gas emission prediction of similar tunnels.