An integrated implementation solution and theoretical framework of fault diagnosis approach based on probabilistic signed digraph (PSDG) is proposed and applied to a gas fractionation unit. On the basis of the primary method of PSDG presented in our previous work, a complete framework of PSDG is constructed, including its definition and reasoning to its implementation. Nodes and branches in PSDG contain uncertain information and their a priori conditional probabilistic parameters are decided by using little knowledge of the studied plant; thus, a PSDG model can be built properly. After cycle processing and model simplification, PSDG reasoning can be conducted approximately on the basis of consistent rule. In implementation of PSDG, the probabilities of candidate faults can be computed and arranged, and the most possible fault is found. Therefore the real fault cause can be further confirmed reasonably. Compared with the conventional qualitative SDG, the qualitative ambiguities in PSDG can be reduced to some extent. The proposed method is applied to a gas fractionation unit, and experimental results on real operation data show the validity and advantages of the PSDG framework.