The reliability of a material transportation system with various kinds of storage rooms can be ascribed to the reliability of soft concatenations in directed trees.This paper puts forward the concept of soft concatenations and gives the mathematical description of how storage rooms improve the reliability function of directed trees.The paper also gives the calculation method of the reliability of soft concatenations and,combining the application to a domestic large-sized coal mine,it tests and verifies the effect of soft concatenations on the increase in the relia-bility of directed trees.