One　typical　two-dimensional　transition　metal　dichalcogenide　(TMDC)　called　the　TcSe2　monolayer　has　been　predicted　to　be　a　potential　photocatalyst　for　water　splitting　hydrogen　production.　In　this　work,　we　have　systematically　studied　the　dynamical　stability,　optical　properties,　energy　evolution　of　adsorption,　and　decomposition　of　water　molecules　as　well　as　the　hydrogen　production　process　of　TcSe2　monolayer　based　on　density　functional　theory.　The　admirable　stability　of　TcSe2　monolayer　in　aqueous　environment　is　proved　by　the　ab　initio　molecular　dynamics　simulations.　We　have　demonstrated　the　energy　evolution　of　the　adsorption　and　decomposition　of　water　molecules　on　the　2D　TcSe2　surface,　as　well　as　the　hydrogen　production　process.　It　is　worth　noting　that　the　distinguished　effective　sunlight　energy　conversion　for　the　TcSe2　monolayer　of　6.17%　suggests　its　potential　applications　for　photocatalysis　and　optoelectronics.　©　2017,　Springer　Science+Business　Media　B.V.