The　high　entropy　alloys　(HEAs)　is　a　kind　of　innovative　alloy　design　conception.　However,　seldom　quantitative　thermodynamics　descriptions　were　reported　in　the　past.　In　this　paper,　as　a　demonstration,　the　microstructures　and　thermodynamic　properties　of　CoCrCuFeNi　HEA　were　studied　by　combining　experimental　approaches　with　computational　simulations.　The　CoCrCuFeNi　alloy　shows　duplex　FCC　structure　with　Cu-lean　and　Cu-rich　phase.　With　the　increase　of　heat　treatment　temperature　from　773　K　to　1273　K,　the　predicted　total　configurational　entropy　changes　from　6.13　to　7.83　J.mol(-1).K-1,　which　is　far　less　than　the　common-believed　Boltzmann＇s　hypothesis　value　(13.38　J.mol(-1).K-1)　due　to　the　ordering　behavior　of　element　occupying　on　the　sublattices.　Cu　atoms　tend　to　enrich　in　liquid　phase,　which　segregates　as　interdendritic　microstructure　during　solidification　process.　The　experimental　results　are　highly　consistent　with　the　calculated　results.