Taking a largespanned tunnel on a highway as an example, the article describes the variations of the pressures and deformations of the surrounding rock mass caused by the tunnel excavation. By means of analysis on the measured data, guidance is provided for the adjustment of the reinforcement parameters during the tunnel construction. By means of comparison with the theoretical formulas, proper formulas are selected, accurate geological parameters are determined and the pressures and changes of the surrounding rock mass ahead of the working face are predicted.