Sea level rise has important implications for coastal regions. In this study, seasonal and interannual variations of sea level in the Bohai Sea and Yellow Sea (BYS) from 1993 to 2017 are investigated using the reanalysis product Estimating the Circulation and Climate of the Ocean (ECCO). Sea level is comprised of two major components: steric sea level and ocean bottom pressure (OBP). On seasonal time scales, steric sea level and OBP have considerable contributions to the sea level variations in the BYS. The sea level in the deep water is linked to steric sea level, while OBP controls the coastal sea level. Diagnostic analysis further suggests that the steric change is owing to temperature change. The OBP variability is dominated by the Ekman divergence/convergence forced by local wind. On interannual timescales, the contribution of steric effect is indiscernible, and OBP dominates the variability of sea level in the BYS. The interannual variability of OBP is forced by wind-induced Ekman transport, and is closely related to the North Pacific Oscillation (NPO) during wintertime. Moreover, Kuroshio has a negative relation with the interannual variability of spring sea level via controlling water volume transport from the Pacific Ocean to the BYS. This study sheds light on the mechanism of sea level low-frequency variability in the BYS, and complements the dynamic processes along the coast.