In order to improve the efficiency and quality in rough milling for open blisks, the plunge milling strategy is a good choice instead of the traditional 5-axis point milling and flank milling for deep and narrow channels machining. Theory and procedures of using a ruled surface to approximate a freeform surface are presented based on the theory of minimum area. The plunge milling strategy is discussed and developed for open blisks. And the NC programs of plunge milling is further developed and verified based on the UG software. At the end, the open blisk test piece was machined by plunge milling. The result reveals that high-speed plunge milling has increased efficiency greatly in the open blisks rough milling than the traditional methods.