Abstract: A shell structure for a thyristor trigger unit comprises an integrally-formed shell body with a holder and a cuboid structure, and a side plate. The cuboid structure is a cuboid with an opening in its front where an open face is formed at the front opening of the cuboid. The cuboid further includes a rear panel, a left panel, a right panel, an upper panel, and a lower panel. The holder includes a square retaining plate and two triangular stiffener plates. The square retaining plate is formed by a bottom panel extending towards a side of the left panel in a long side direction of the cuboid while the triangular stiffener plates are fixedly connected between the square retaining plate and the left panel. The side plate is mated with and detachably mounted on the open face to produce a sealed 6-face cuboid structure by sealing off said open face.