We numerically investigate the electronic band structure of carbon nanotubes (CNTs) under radial corrugation. Hydrostatic pressure application to CNTs leads to a circumferential wave-like deformation of their initially circular cross-sections, called radial corrugations. Tight-binding calculation was performed to determine the band gap energy as a function of the amplitude of the radial corrugation. We found that the band gap increased with increasing radial corrugation amplitude; then, the gap started to decline at a critical amplitude and finally vanished. This non-monotonic gap variation indicated the metal-semiconductor-metal transition of CNTs with increasing corrugation amplitude. Our results provide a better insight into the structure-property relation of CNTs, thus advancing the CNT-based device development.