We report stray light simulation for the current GOCI and proposed next generation ocean color instruments GOCI-II. GOCI is a TMA system of 140mm in aperture and GOCI-II is a Cassegran telescope based system of about 300mm in aperture. Both instruments are designed to provide 500 m and 200 m in spatial resolution respectively. During in-orbit measurement operation, these instruments are exposed to sun light illuminating the Earth surface. The instrument aperture is then filled with the incident stray light originated from around the measurement target. We built complete 3D optical models of GOCI and GOCI-II with realistic optical characteristics. A full 3D optical Earth model was also built using the world coastal line data of 15km in spatial resolution. The Sun was modeled in real scale for both geometric size and radiative power. These components were integrated into a Monte Carlo ray tracing computation for source-to-detector radiative transfer. The stray light levels were then estimated for possible orbital configurations for in-orbit measurement operation. The study presents analysis model building, details of stray light computation and results.