Abstract: The coordinating function between the primary supporting and the broken rock has the prominent character of uncertainty. The main effecting factors are as follows: the non-uniformity of primary supporting coming from the construction, the effect coming from the uncertainty of actual surrounding rock, the uncertainty of internal force distribution in primary supporting coming from the non-uniformity of releasing stress on surrounding rock. The retaining of primary supporting and the self-stabilization capability of rock are regarded as a dual-media (i.e., the bearing complex model). The displacement objective function is constructed by the least square formulas. Combining with the optimization method of simplex, the model with the bearing complex is applied to back-analysis of road tunnel. The results reveal the coordinating function between the primary supporting and the broken rock zone. In contrasts to the inversion result without considering the uncertainty of the primary supporting, the accuracy of inversion is improved 39% and the accuracy of prediction is improved 13%. Thus, The proposed method and the results can be used as reference to the construction and design of road tunnel with similar conditions.