Ordered mesoporous carbons (OMCs) with tunable mesophase were prepared by a novel cosolvent method using low molecular resin as carbon precursor, and P123(Poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide)triblock copolymers, EO20PO70EO20) as a template via an Evaporation-induced Self-assembly Process (EISA). The results show that the pore structure of OMCs could be oriented from 2D hexagonal (p6mm) to 2D centered rectangular (C2mm) structure. Two key descriptors of mesophase were identified. One is the ratio of PEO/PPO of triblock copolymer, and the other one is cosolvent, both of which would have effects on the interface of mesophase during the EISA process. Furthermore, it was confirmed that the ordered mesophase could be obtained in a very short time during the EISA process even accompanied by the microemulsion phenomenon.