Abstract: The atmospheric quasi-biweekly oscillation (QBWO) is one of the dominant intraseasonal modes in tropics and subtropics, which is critical for improving extreme weather forecast in a 10-20 days extension period. Compared with comprehensive understanding of the QBWO in the Asian monsoon regions during boreal summer, studies focusing on the austral summer QBWO in the southwestern Indian Ocean are relatively scarce, particularly on the oceanic feedback processes of SST perturbation. This study utilizes atmospheric reanalysis data and observed SST data from 1981 to 2022 to quantitatively evaluate the key oceanic feedback processes of SST perturbation on QBWO through moist static energy (MSE) diagnosis and sensitivity experiments. The results indicate that the summer QBWO events in the southwestern Indian Ocean can be divided into two modes based on their propagation paths: southward and eastward propagation. The development and evolution of both modes are closely related to the evolution of MSE, i.e., the enhancement (weakening) of QBWO convection accompanies a significant recharging (discharging) process of MSE, which is primarily controlled by horizontal advection term. The feedback of SST perturbations on the turbulent heat fluxes through sea surface is more significant in the southward propagation mode of QBWO, where the changes in latent (sensible) heat flux induced by SST perturbations can account for 12.5% (3.5%) of the MSE temporal change rate, or 16% in total. In contrast, in the eastward propagation mode, the turbulent heat fluxes caused by SST perturbations can only account for 2.6% of the MSE temporal change rate.