Deep ultraviolet (deep-UV, 200nm~300nm) spectrum analysis is an important technique in underwater biochemical sensors. For in-situ exploration, integrated optics based wavelength selective light source would have advantages in obtaining high sensitivity spectrum, compactness and low power consumption. The key components used in forming such wavelength selective light source are optical switch and bandpass filters. However, such optical switch and bandpass filter in deep-UV band have rarely been studied, to our best knowledge. In this paper, we proposed and designed a silica-based optical waveguide structure that can achieve single-mode transmission at 210nm-240nm. Furthermore, we designed and simulated a Mach-Zehnder Interferometer (MZI) switch in deep-UV band for in-situ marine chemical sensing application. In our simulation, a rectangular optical waveguide with single-mode operation has been achieved based on phosphorus (P) and boron (B) co-doped Silica core waveguide with 2.9μm in width and 0.35μm in thickness. The refractive index difference between core and cladding layer is Δn=0.003. Based on this waveguide structure, we also designed a Mach-Zenhder interference (MZI) type optical switch with extinction ratio larger than 26dB at deep-UV band.