Engineers designing axial and radial turbomachines have applied completely different deviation or slip factor models. When designing a mixed-flow impeller, which lies between the ranges of conventional axial and centrifugal flow and displays fluid dynamics features of both radial- and axial-flow, one has to choose between axial or radial slip models. Qiu give a unified slip factor model that can be applied to axial, radial and mixed-flow impellers. This model has been validated successfully in applications of axial and radial impellers but no validation with mixed-flow impellers. Experimental data of mixed-flow impeller are provided to compare with slip factors calculated by the new model. The validations show that the new model predicts slip factor of mixed-flow impeller well in general cases except on the condition of high flow coefficient and the new model provided a good choose for mixed-flow impeller design.