Aiming at the disadvantage of failure risk assessment using risk priority number (RPN), the semi-quantitative method using fuzzy variable weight synthesis and analytic hierarchy process (AHP) was brought forward. The model of the risk assessment was divided into two layers. Firstly, according to the production loss, repair costs, safety and environment impact, fuzzy AHP and encouragement variable weight synthesis were introduced into the quantitative assessment of failure severity to improve its accuracy and objectiveness. Then, via severity, occurrence, and detection, variable weight and AHP were adopted for failure mode risk assessment to make assessment results closer to the reality. At last, an instance was provided to illustrate the potential applications of the proposed model. The result shows the proposed approach is effective and feasible.