Abstract: The heteroepitaxy of diamond films has received widespread attention; however, its application remains limited owing to the mismatch in properties and structure between diamond and heterogeneous substrates. In this study, diamond films were successfully synthesized on high-entropy alloys (HEAs) substrates using microwave plasma chemical vapor deposition. The resulting diamond films were continuous, uniform, and adhered to the HEAs substrates. The mixed carbides were identified using X-ray diffraction, and the quality of the diamond films was examined using Raman spectroscopy. Moreover, the corrosion test revealed that the diamond/TiZrHfMo samples had excellent electrochemical stability and corrosion resistance with a corrosion potential value of −0.169 V in a 3.5wt% NaCl solution. A multiple regression model was established to evaluate the effects of the structure and growth parameters, which confirmed that the mixing entropy significantly affected the grain size and corrosion properties.