SDL (CCITT Functional Specification and Description Language) is designed mainly for telecommunication. According to the CCITT SDL'88 documentation, this paper designs and implements the SDL Supporting System (3S) based on Graphical Kernel System (GKS). The 3S can be used to edit SDL document in graphical representation (SDL /GR), then check the correctness of the document, and at last translate the graphical document into phase representation (SDL/PR). 3S made it possible to specify and describe user's requirement in graphical method and get the text result, or high level languages.