The invention provides a fault diagnosis method of a hydrometallurgy thickener based on credibility. The method includes obtaining on-line variables of a hydrometallurgy thickener; determining fuzzy dimensionality of each variable according to on-line variables, wherein the fuzzy dimensionality is dimensionality corresponding to fuzzy concepts included in rule antecedents in a pre-established expert rule base; aiming at each variable and the fuzzy dimensionality of the variable, adopting a fuzzy membership degree function to obtain the credibility of the fuzzy dimensionality to which the variable belongs; based on an uncertainty reasoning model based on credibility and rules in the expert rule base, performing rational analysis on the credibility of each variable, and obtaining fault conclusion credibility; and comparing the fault conclusion credibility with a preset threshold value, and obtaining a fault result. The abovementioned method can obtain rules corresponding to diagnosis experience of experts or operating personnel in advance, and perform fault diagnosis on current on-line variables, so as to perform timely adjustment according to a fault diagnosis result, thereby effectively reducing an accident rate, and improving production safety.