We investigated the effect of electrochemical hydrogen charging on the surface integrity of high-entropy alloys (HEAs). Two types of HEAs with stable (CoCrFeMnNi) and metastable (Fe50Mn30Co10Cr10C0.5) phases were tested by using in-situ electrochemical nanoindentation and scanning probe microscopy techniques in combination with advanced characterization and post analysis. After only hydrogen charging, surface slip line formation was observed on CoCrFeMnNi, while austenite to martensite transformation was detected on Fe50Mn30Co10Cr10C0.5. The hydrogen-induced internal stress is proposed to be responsible for the surface integrity change upon hydrogen charging, and this internal stress might be a potential driving force to the environmental failure of HEAs. It is necessary to consider these effects in future studies on hydrogen embrittlement and the design of hydrogen-tolerant alloys.