<p>Resolving the regional ocean circulation is a key factor in the understanding of climate-driven oceanic variability. Accurate sea level simulation, in the areas at the interface between land and ocean, could help to mitigate the environmental, social and economic damages caused by sea level rise and extremes. This is particularly the case for the seas in the Southeast Asia region (SAR), where the ocean circulation is complex owing to unique geographic and oceanographic features of the region. In order to overcome the caveats due to sparse sampling of this domain regional configuration of the ocean model (NEMO) is set up for the SAR (90<sup>o</sup>E-142<sup>o</sup>E; 18<sup>o</sup>S-26<sup>o</sup>N) with 51 vertical sigma levels and hindcast simulations are performed for the period 1958–2021 using the downscaled ERA5 (surface forcings) and ECMWF global ocean reanalysis (ORAS5) data as lateral boundary conditions. This paper describes the dominant phenomena and model performance in simulating the low-frequency variability of the seas in the SAR with a focus on sea level, SST and ocean currents. The comparison of simulations with tide gauges and satellite altimetry observations yields good match. Correlation analysis between the simulations and air-sea coupled phenomena like El Nino southern Oscillation (ENSO) and Pacific decadal oscillation (PDO) reveals significant correlation which provides the confidence for further research of the low-frequency ocean variability in the SAR.</p> <p><strong>Keywords:</strong> Validation (SSH) with Tide-gauges, Satellite, SST with Reanalysis, Observation, Maritime Continent</p>