Abstract: To identify the variation of viscosity of WF heavy oil mixed with diesel, blank WF heavy oil is mixed with diesel with different mass fractions of 5%, 10%, 15%, 20% and 25%, for purpose of measuring the apparent viscosities of blend oil at different temperatures. The test results are compared with the prediction results with applicable viscosity calculation models, indicating that Walther viscosity-temperature correlation is appropriate for describing the relationship between viscosity and temperature of the blend oil, while results of Chirinos model, Shu model and Miadonye model cannot meet the needs of the practical engineering. Using the back calculated c value, Cragoe model can be used for viscosity prediction of WF heavy oil mixed with diesel, and the average relative deviation is less than 5%. Therefore, based on Cragoe model, a reliable and convenient viscosity prediction method for WF heavy oil mixed with diesel is proposed, which is applicable to practical engineering.