Based on the OFES simulation results with a horizontal resolution of 1/30(°) from 1991 to 2019, this study investigates the interannual variability characteristics and regulatory mechanisms of submesoscale kinetic energy (KE) in the northeastern South China Sea (SCS). By calculating the submesoscale KE, it is found that the submesoscale KE in the northeastern SCS exhibits significant interannual variability, with a general periodicity of 3~5 a. Correlation analysis reveals that the interannual variability of submesoscale KE in this region is jointly modulated by the mesoscale strain rate (MSR) and mixed layer depth (MLD). Among these factors, the flow field strain associated with mesoscale eddies is the primary driver of the interannual variability in submesoscale KE, while the contribution of MLD is relatively weaker. Further research indicates that the Kuroshio path in the northeastern SCS during winter plays a crucial role in the intensity of submesoscale KE. When the Kuroshio intrusion exhibits a Looping pattern, the mesoscale strain rate significantly increases, and submesoscale processes become more active. The interannual variability characteristics and regulatory mechanisms of submesoscale KE revealed in this study provide valuable insights for further research on multi-scale dynamic interactions and energy cascade processes in this region.