A thermomechanical model for oblique cutting was proposed. Using equivalent plane approach, orthogonal cutting theory based on unequal division shear zone was extended and applied to oblique cutting. The orientation of the equivalent plane was determined by the equivalent plane angle. The geometrical parameters associated to oblique cutting were analyzed using the coordinate transformation approach. The governing equation of the shear velocity, shear strain, shear stress and temperature distribution in the shear zone were established. The flow stress was predicted from Johnson-cook material constitutive equation which considered the effects of strain hardening and thermal softening. At last, the cutting forces were calculated for different machining conditions, predicted results are in good accordance with oblique cutting test data from the available literature and found. The proposed model can be used to predict cutting force of end milling by the experimental validation.