Abstract: The atmospheric quasi-biweekly oscillation (QBWO) is one of the dominant intraseasonal modes in the tropics and subtropics, which is an important basis for improving the extreme weather forecast in the 10-20 days extension period. Compared with comprehensive analyses 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 process of SST perturbations. This study utilizes atmospheric reanalysis data and observed SST data from 1981 to 2022 to quantitatively evaluate the key oceanic feedback process of SST perturbations on QBWO through moist static energy (MSE) diagnosis and sensitivity experiments. The results indicate that 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 the horizontal advection term. The feedback of SST perturbations on the turbulent heat fluxes at the 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, totaling 16%. 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.