Abstract: Fixed value judgement method is mostly applied in surrounding rock stability forecasting at present, but those factors that affect the surrounding rock deformation are so many and mutual restrictive, so that determination of an accurate definite value is extremely difficult. To avoid the problem how to determine a fixed value in fixed value judge method, this article, based on the data collected from some tunnel monitoring and measurement, uses gray theory and fuzzy probability method to analyze and calculate the tunnel surrounding rock stability and stability probability, and makes stability problems mathematization, so that it can exactly reflect surrounding rock stability state. The results show that forecasting the final deformation of surrounding rock is accurate by using the gray theory, and analysis of the surrounding rock stability is reasonable. It can timely provide stable degree of surrounding rock and security information of structural reliability, predict accident and dangerous situation. The process of the calculation is simple, convenient in projects applications.