It is vital to develop a high activity, stability and inexpensive hydrogen evolution reaction (HER) catalyst for electrochemical hydrogen evolution. A high-temperature reaction approach that is Co nanocrystals on carbon support (XC-72R) and selenylation to synthetize CoSe2/C nanocrystals is used, and the effect of temperature on CoSe2/C nanocrystals is studied. The morphology and catalytic properties of CoSe2/C nanocrystals annealed at different temperatures are compared in 0.5 M H2SO4. The results indicated the corallinelike CoSe2/C-650 nanocrystals have a high performance for HER with Tafel slopes of 45.73 mV.dec(-1) and onset potential of -196 mV vs. RHE. The stability maintained for at least 40 h and the Faraday Efficiency (FE) of H-2 is nearly 98%. The outstanding HER performance of CoSe2/C-650 is due to its characteristic cora-like frame CoSe2 nanocrystals embedded into supernal conductive XC-72R, which not only offer affluent active reaction sites, but also boost the capacity of charge transportation in HER process. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.