The invention belongs to the filed of Longmen machine tool devices in the mechanical manufacturing industry, in particular to an upright post/beam composite guide rail structure of a digital-control Longmen machine tool, comprising a beam, a left upright post and a right upright post, wherein the left upright post is matched with the beam by a left guide rail device in a sliding way, and the right upright post is matched with the beam by a right guide rail device in a sliding way; the left guide rail device is provided with a datum guide rail device comprising a plurality of datum guiding devices and a left guide rail, the datum guiding devices are matched with the left guide rail in a sliding way and are fixedly arranged at one end of the beam, and the left guide rail is fixedly arrangedat one side of the left upright post; the right guide rail device is provided with an adjusting guide rail device comprising a plurality of adjusting devices and a right guide rail, the adjusting devices are matched with the right guide rail in a sliding way and are fixedly arranged at one end of the beam and the right guide rail is arranged at one side of the right upright post. The invention has the advantages that the precision and the bearing capacity of the guide rails are improved, the loss is reduced, the service life of the guide rails is prolonged, and the production cost is decreased.