Key Points:  A new mean sea surface model with a grid of over the Sea of Japan and its adjacent ocean (named SJAO2020) is established  The new altimetry data of HaiYang-2A, Jason-3 and Sentinel-3A have been used in establishing the SJAO2020 model  Tide gauge stations and joint GNSS are used to improve the offshore accuracy of the SJAO2020 model. Abstract The mean sea surface (MSS) model is an important reference for the study of sea level change and charting data, and the coastal accuracy of the model has always been the focus of marine geophysics and oceanography. A new MSS model with a grid of over the Sea of Japan and its adjacent ocean (named SJAO2020) (25°N~50°N, 125°E~150°E), is established from a combination of 26 years of satellite altimeter data from a total of 12 different satellites and records of 24 tide gauge stations and joint GNSS data covering the period 1993-2018 by a 19-year moving average method. Different from the latest international MSS models CLS15 and DTU18, the data of the latest altimetry satellites HY-2A, Janson-3 and Sentinel-3A are also introduced, and tide gauge records as well as the joint GNSS data are used to correct the SSH within 10 km from the coastline by using the Gaussian inverse distance weighting method in the SJAO2020 model. By comparing with tide gauge records, satellite altimeter data and other models (DTU18, DTU15, CLS11 and WHU13), it can be demonstrated that the SJAO2020 model produces the smallest errors, and its offshore accuracy is relatively reliable.