Abstract: In order to establish a better rock mass quality grading system and improve the traditional grading methods and other mathematical evaluation methods, a matter-element model based on extenics theory for rock mass quality grading evaluation is established in combination with the engineering geological conditions of navigation tunnel in Hongyan Reservoir. The grey relevance method is used to improve the subjective and objective factors for calculating the weight of each evaluation index in extenics theory. The results showed that the subjective and objective factors of rock mass quality evaluation are fully considered by the grey relevance method, and the weights of each index calculated were reasonable and reliable. The combination of grey relevance method and extenics theory could not only reflect rock mass gradation, but also reflect the distance between different grades. The application of this theory to classify and evaluate surrounding rock quality would have definite guidance in engineering practices.