This paper presented a study of the relationship between cutting force and tool flank wear of solid carbide tool during the wet end milling Ti6Al4V. The modeling of 3D cutting force in end milling considering tool flank wear was discussed, which showed that for the given cutting conditions, tool geometries, and workpiece material, cutting force under the tool flank wear effect can be predicted easily and conveniently. In addition, the experimental work of end milling Ti6Al4V with solid carbide tool was developed to investigate the relationship between cutting force and tool flank wear, and comparison between experimental results and predicted results was discussed. The results showed that the proposed mathematical model can help to predict 3D cutting force under the tool flank wear effect with high accuracy.