As a new theory of managing incompatible problems, extenics has been increasingly applied in engineering field widely. In this paper, based on the theory of extenics, the matterelement model for the stability evaluation of stope roof of the underground mine is established and the stability of No. 92 orebody in TongKeng mine of DaChang is evaluated. Through the determination of factor weight by using simple dependent function and the calculation of the dependent degree, objective and reasonable results are gained. It is proved that the evaluation of the complex and uncertain rock engineering used by extenics theory is effective and feasible.