The simulation of global and regional energy system transition and its potential mitigation cost could intuitively reflect the need for earlier climate mitigation actions.To explore the possible transitions of global and regional energy system,this study applied a 14-region energy system model (GTIMES) with scenarios designed using Shared Socio-economic Pathways (SSPs) with Representative Concentration Pathways (RCPs),and detailed depicts the quantification of SSPs trajectories into GTIMES model.Modeling results show that:1) Global energy-related CO2 emissions will reach 37-74 Gt by 2050 under reference scenarios,while they will decrease to 12-14 Gt under higher possibility pathways to reach 2 ℃ target,with ratios of non-fossil fuel round to 42％-46％.2) Electrification level has to increase noticeably in regional transition with a global average level of about 44％ to achieve significant emission reduction.3) Higher level of mitigation cost would happen with the constraint mitigation target,as well as social and economic trajectories chosen.Therefore,following trajectories of sustainable development is necessary.