In this paper Finite element methods (FEM) and cutting experiment were used to investigate the machinability of titanium alloy ZTC4 (cast Ti6Al4V). Machinability was evaluated as cutting force, temperature, and surface roughness. Two-dimension (2D) and three-dimension (3D) machining process FEM models were established. Material constitutive applied Johnson-Cook model synthesizing elastic and plastic deformation. Chip separated criteria adopted arbitrary Lagrangian Euler (ALE) algorithm. Heat generation source included the rake face chip flow under conditions of seizure and chip/tool friction, clearance face tool/workpiece friction. 3D discrete milling tool was modeled and the milling process was simulated. The ZTC4 milling experiments were designed and carried out with same cutting conditions of the 3D FEM simulation. The results of FEM simulation and the experiment were compared and analysed. The influences of the machining variables to the machinability of ZTC4 were discussed.