Abstract: With the development of dome roof oil tank to big diameter, the variable support of shell comes inta being because the application of dome roofs with rib is limited by its diameter. In API 650 Appendix G, the theory and formula of design method for the aluminum dome roof are given, which is suitable to the steel dome roof. On the basis of API 650 Appendix G, this paper analyzes and discusses the structure and its application of the space truss.