Transparency is one of the critical indicators for marine ecological environment monitoring, and it plays a vital role in the military, navigation, fishery, and other fields. Compared with other traditional ocean monitoring technologies, remote sensing technology has the advantages of long time sequence, extensive range, and near real-time acquisition of ocean information. Therefore, it is of great significance to the rational development and utilization of marine resources by using satellites to observe ocean transparency. This study used the in situ transparency data and the equivalent remote sensing reflectance data of the Sentinel-3 OLCI sensor to build the Bohai Sea transparency inversion model, which mainly included the single band method, the band ratio method, and the mixed band method. The model’s accuracy was verified with the in situ-satellite match-ups. It found that the best inversion model was the mixed band model with B6 (560 nm) and B7 (620 nm) as the sensitive factors. The coefficient of determination R² was 0.68, the average relative error (MRE) was 15.93%, and the root means square error (RMSE) was 0.48 m. On this basis, combined with Sentinel-3 OLCI time-series images, we got the monthlyremote sensing products of Bohai transparency in 2020 and found that thetransparency showed obvious regional and seasonal characteristics. The transparency ranged from 0 m to 10 m. It was higher in July and August. The value of some areas could be deeper than 9 m. While it was relatively low in winter, the value was less than 2 m in January and February. At the same time, we also found that the higher transparency appeared in the central Bohai Sea and the coastal waters of Qinhuangdao, while the transparency was lower in Bohai Bay, Liaodong Bay, and Laizhou Bay throughout the year. The characteristic trend of transparency is inseparable from Bohai Sea coastal geological properties, the distribution of surrounding rivers, and coastal urban agglomerations and industrial ports. This research provided a reliable theoretical basis for remote sensing transparency estimation, and it was of great significance for monitoring the marine environment of the Bohai Sea.