Based on the practical measurements during tunnel construct ion, the specimen parameters of over-excavating and under-excavating for E，IV﹠V scries of surrounding rocks arc obtained. The numerical characteristics and the probability distributions of over-excavating and under-excavating for different series of surrounding rocks are put forward through numerical and physical statistics and analyses.At the same time,the law of distribution of over-excavating and under-excavating at different portion on tunnel section for different series of surrounding rocks are also obtained,which may be used for controlling the quality of construction and taken as reference for researching the reliability of the tunnel Structure.