The analysis of the mechanism of cutting tool wear in high speed machining of cast aluminum alloys is conducted in this research work. The result of analysis indicates that the interaction between the hard silicon constituencies of the alloy and the surface of the cutting tool is the most detrimental to tool life. The wear of the cutting tool in such interactions, governed by fatigue wear mechanism, is directly proportional to silicon content of the alloy, silicon grain size and to the tool’s loading conditions. In order to predict the tool wear in machining aluminum cast alloys, a new wear model is developed. The fracture mechanics approach in wear rate estimation is implemented in this model. As an input data for the tool wear modeling, the normal and tangential stresses, acting on the flank of cutting tool are used. The fracture mechanics analysis of the subsurface crack propagation in the cobalt binder of cemented carbide cutting tool material is performed using a finite element (FE) model of the tool-workpiece sliding contact. The real microstructure of cemented carbide is incorporated in the FE model of tool-workpiece contact, and elastic-plastic properties of cobalt, defined by continuum theory of crystal plasticity are introduced in the model by UMAT subroutine of the ABAQUS® FE software. The crack propagation rate, determined from FE modeling, is used then in the model of cutting tool wear, developed in this work. This model is capable to predict the wear rate of cutting tool, base on the microstructural characteristics of the cutting tool and workpiece material and the tool’s loading conditions. The model can be used for cutting tool life assessment and management in high speed machining of Al-Si alloys in an industrial setting.