This series machine, which can realize dual- side or tri -side synchronized milling, is a kind of high efficient milling equipment developed by us. The upper press- beam can move backward wholly, which is convenient for loading and unloading of work- -piece. It is equipped with four or five sets of milling unit and feeding device, which can be controlled separately or together. It can synchronous or single side mill the plate with high straightness and parallelism. This equipment is widely used in the milling of U- rib for steel bridge or batch production of large work -piece.