Abstract: In view of the application of reticulated shell structure in coal industry, the design of flat space truss on plant roof is introduced, and the definition of constraint state of support of flat space truss is analyzed.The equivalent spring stiffness of cantilever column support is solved by using the theory of material mechanics.The calculation method of tangential and normal support constraint state of grid support is clarified.Taking the roof of the main power house of Ji Lang De open pit coal mine as the engineering background.According to the calculation results of general finite element software of 3D3S design 2021 structure, the stress conditions of space truss under two different support constraints are discussed.