Obilque cutting of wood is an important form of cutting wood. With the developing of woodworking industry, it is widely used in wood machinary processing such as planing, milling, sawing, drilling and so on. This paper takes oblique planing and helix milling of wood as examples. The influences of bevel angle and other factors on the cutting force have been shown. The changing rules of cutting forces have been summarized. On the basis of it, we especially carried out theoretical analysis on the changing rules of cutting forces and discussed the influence of the changing rules on practice.