Carbon　nitride　(CN)　polymer　has　been　widely　investigated　as　a　photocatalyst　for　solar　hydrogen　production　in　recent　years　due　to　its　unique　properties.　However,　the　pristine　CN　typically　shows　moderate　photocatalytic　performance.　An　important　reason　is　its　high-density　defects　in　CN　framework,　and　it　could　play　the　role　as　a　recombination　center　of　photogenerated　electron-hole　pair.　Therefore,　increasing　the　crystallinity　can　be　one　of　efficient　way　to　enhance　its　photocatalytic　activity.　Recently,　we　have　report　a　new　heptazine-based　crystalline　CN　synthesized　by　ionothermal　method,　and　the　as-prepared　sample　has　been　exhibited　high　activity　toward　photocatalytic　hydrogen　production.　Herein,　we　systematically　investigated　influences　of　the　synthetic　temperature　on　the　properties　and　photocatalytic　activity　of　the　as-prepared　crystalline　CN　polymer.　Our　results　demonstrate　that　the　crystalline　CN　synthesized　by　using　550　°C　pre-heated　precursor　shows　the　highest　activity　in　photocatalytic　hydrogen　production,　and　achieving　an　apparent　quantum　yield　of　6.8%@420　nm　with　MeOH　as　sacrificial　agent.　When　compared　to　the　reference　photocatalyst　P25,　the　CCN550　shows　remarkable　photocatalytic　hydrogen　production　under　visible　light　irradiation,　while　P25　is　virtually　inactive.　In　addition,　the　amount　of　produced　hydrogen　gas　by　CCN550　is　closed　to　P25　under　full　arc　irradiation　of　Xe　lamp,　which　highlights　the　potential　solar　energy　utilization　of　such　crystalline　conjugated　polymer　in　the　future　development.　©　2018　Elsevier　B.V.