Abstract: In order to realize optical detection of underwater vehicle, the mechanism of optical properties measurement of underwater environment is studied, and measurement method for ocean downward radiation and upward radiation is established. Based on the analysis of distribution law of ocean downward radiation, the ocean downward radiation model is simplified, Janus ocean downward irradiance measurement model is established, the irradiance optical probe is designed, the ocean upward radiation measurement method is determined, and the optical probe response scale is designed. Results show that downward irradiance is determined by scalar irradiance, scattering coefficient, volume attenuation coefficient and diffuse attenuation coefficient. The incident angle is the incident radiance. When incident angle is less than 70 °, cosine error is less than 5%. Measurement of ocean downward irradiance is optimized by Janus design. The establishment of ocean downward radiation and upward radiation measurement method has laid a technical support for underwater visualization of target environment.