Abstract: Based on experience，the preferred faults controlling the regional stability of large engineering can be classified by using the gray correlation degree an analysis method．According to the recognition rule of the biggest correlation degree this method determines the grade of preferred faults by referring to the preferred indices which includes time index(RT)，dimension index(RL)，distance index(RD)，activity period index and activity history index(RR)and comprehensive index(RZ)． The old evaluation methods are more complicated and the boundaries between two preferred indices are not dear．The present analysis method overcomes the above-mentioned shortcoming and can be used in the evaluation of preferred faults and expert system of preferred plane．