Abstract: The runout of milling cutter is a form of milling vibration, which not only increases tool wear, reduces the processing quality, but also makes cutting tool chipping or fracture. Based on experiments of micro end milling straight groove, the basic characteristics of milling cutter runout is revealed. The influence rule of milling parameters on cutter runout is studied and the nonlinear relation model between milling parameters and cutter runout is built. The result show that, the order of milling cutter runout in three direction is as followed: Width direction of groove＞feed direction＞axial of end milling cutter; milling parameters are the main factor that influence the cutter runout, their significance level is as follows：Milling speed vc＞axial cutting depth H＞ feed velocity f; the nonlinear relation model built by orthogonal test has a good fitting effect and can be used to forecast and control the milling cutter runout.

Key words: micro end milling;straight groove;cutting parameter;milling cutter runout