In traditional fiveaxis linkage numercial control (NC) machining, the ball end milling cutter is usually used to machining curved surface. But as the hyperboloid surface is more and more complex, the ball milling cutter head is exposed of more and more disadvantages than flatbottomed cutter. So it was replaced by flatbottomed cutter to improve the shortage of the ball end milling cutter. When using flatbottomed cutter machining hyperboloid, the knife trajectory planning is complex and difficult because of the change of surface curvature everywhere. Making greatly affects on its application in machining surface. Therefore, how to plan the knife trajectory was researched based on using flatbottomed cutter to machining hyperboloid on the fiveaxis machine. The cutter location point of knife trajectory was gotten by calculation, and designed the knife tractectory planning method. The results show that the method improves the shortcomings in machining, precision and working efficiency of the fiveaxis machine machining surface when using bll end milling cutter.