The estimation of country rock stability in underground engineering is the important basis for carrying out engineering design and formulating corresponding engineering measures. The interval form of quality standard, the value of resolution coefficient ρ and the weight of correlation degree are seldom takend consideration by the traditional gray correlation analysis model, an improved gray correlation analysis model is used to analyze the five indices of influencing the country rock stability: rock quality designation RQD, moisture compressive strength Rw, integrity coefficient Kv, structure surface strength coefficient Kf, groundwater seepage measurement W/L. The results show that the improved correlation analysis model is superior in its objectivity and applicability as well as certain practical value in evaluating country rock stability or other evaluation problems.