In order to obtain more accurate results of rock mass quality evaluation based on extenics engineering method，we established the matter-element model of rock quality evaluation based on the theory of matter-element model.With a review of the various factors of the matter-element of feature given practical domain，calculation formula of interval distance was established as well，and finally we applied extension set correlation functions to establish evaluation method of engineering rock mass based on the content and links function extension.Main engineering rock mass quality of the iron ore was valuated，and the results demonstrated that the rock quality level of N1 belonged toⅠ，while N2，N3 ，N4 as well as N5 were all Ⅱ，and N6 belonged to Ⅲ.Through comparing the results of extension theory and quality evaluation of rock mass obtained by other evaluation，we verified the feasibility and reliability of engineering rock mass quality evaluation method based on feature range.