Abstract: Highly viscous crude oil is commonly transported with mixing technique (heavy crude and light crude) in order to reduce viscosity. However, the viscosity calculation model available to the mixed crude oil remains to be developed. Based on the publications and information, the author develops a viscosity calculation model for mixed crude oil and points out its available scope. Take the Tuha-Nanjiang-Beijiang (heavy crude) mixed crude oil for example, the article introduces the screening course of viscosity calculation models which provides a reference for actual application.