To explore the influence of primary influencing factors on the results of shieldtunneling risk assessment, a riskevaluation model is established based on a combined assignmentnonlinear fuzzy analytic hierarchy process(FAHP). The shieldtunneling process and risk sources are then decomposed using work and riskdecomposition structure methods, respectively, and the two are combined to construct a shieldtunneling riskassessment index system. A multiplicative integration method is used to combine the subjective and objective weights, and a fuzzy relationship matrix is constructed by combining the subordination vector obtained from the expert scoring method. The obtained combined weights and fuzzy relationship matrix are then analyzed by introducing a nonlinear operator. Next, the final risk level of shield tunneling is determined according to the principle of the maximum degree of subordination. The proposed model is applied to the shield tunneling of Phase 1 of the Guiyang Railway Transit Line 3 Project between the Tongmuling and Taohuazhai stations, and the riskassessment results show that the project displays a medium risk level, which is consistent with the risk level in the field.  The proposed model is compared with the conventional FAHP method, verifying the scientificity and reliability of the new model.