Introduction  In voltage sourced converter based ultra-high voltage direct current (VSC-UHVDC) converter station, the roof span of valve hall far exceeds the previous project, and the traditional trapezoidal steel truss structure is no longer applicable.

  Method  In the absence of experience for reference, the structural design of long span roof was studied based on the characteristics of the VSC-UHVDC valve hall, and a reasonable structural type was confirmed. Starting from the number of grid layers, the height of grid, the form of joints and the form of grid, the optimal design of the long span space grid roof was carried out.

  Results  The results show that the optimized three-layers diagonal square pyramid grids roof has good structural performance and economic benefits, and is an excellent structural form the long span roof of VSC-UHVDC valve hall.

  Conclusion  The optimized structure of the grid roof can be used for reference by similar projects.