To design a stream system for corrugated board production line, in order to realize the reuse of secondary steam and reduce the energy cost. The steam system was dismantled into the two basic components, the heating unit and the pipeline, for which mathematical models were constructed respectively. On the basis of the mathematical models, the calculating method for pressure drop of steam system was derived according to the designing alternative of an engineering example. By practical example calculation, the cause for the non-free dewatering in the example was determined. In line with the calculation result of pressure drop, the influence among different pipelines was greatly reduced and reasonable reuse of the secondary steam was realized by rearranging the pipelines in the system. A calculating method of pressure drop for steam system of corrugated board production line was established to provide a theoretical and analytical basis for energy-saving design and troubleshooting on the site, being available for engineering reference.