Abstract: Based on the viscosity data measured from 140 Group of Beijiang Tuha and Shengli Oman mixed crude oil, a research is carried out on the applicability of Lederer Model (experiment constant αuses Indian Shu relational expression). It is found out when using the model to calculate high viscosity vs the viscosity of the mixed crude, there exists a critical temperature; when the temperature of the mixed crude exceeds the critical temperature. Lederer Viscosity Model will show its higher anticipated precision, with 3.97% of its minimum average absolute and relative bias and 9.15% of its maximum average absolute and relative bias. When below the critical temperature, the anticipated precision of the Model will he not all roses evidently, with 13. 57% of its minimum average absolute and relative bias and 109. 8% of its maximum average absolute and relative bias, which can't meet engineering requirements. The critical temperature will vary with different components of the mixed crude and different mixing proportions, generally less than the abnormal point of the highly waxy component oil. Additional finding is that most of the average relative bias of the value anticipated by Lederer Viscosity Model show negative bias, that is most anticipated values are less than the measured value, which indicates that experiment constant ausing Shu relational expression should be corrected further.