Micro-milling tool breakage has become a bottleneck for the development of micro-milling technology. A new method to predict micro-milling tool breakage based on theoretical model is presented in this paper. Based on the previously built micro-milling force model, the bending stress of the micro-milling cutter caused by the distributed load along the spiral cutting edge is calculated; Then, the ultimate stress of carbide micro-milling tool is obtained by experiments; Finally, the bending stress at the dangerous part of the micro-milling tool is compared with the ultimate stress. Tool breakage curves are drawn with feed per tooth and axial cutting depth as horizontal and vertical axes respectively. The area above the curve is the tool breakage zone, and the area below the curve is the safety zone. The research provides a new method for the prediction of micro-milling tool breakage, and therefore guides the cutting parameters selection in micro-milling.