We assess microstructural alterations in superficial white matter (SWM) in cerebral small vessel disease (CSVD) and evaluate their contributions to the decline in processing speed, which is the main dysfunction in CSVD. We identify that the significant decline in processing speed may relate to the involvement of WMH in the SWM under high burden of disease. The increased extracellular free water may be the main SWM microstructural change under low burden of disease. These observations suggest that the SWM may serve as a potential target for monitoring pathophysiological processes in CSVD. This study extends the current understanding of CSVD-related dysfunction.