Abstract: Recently, a new supercritical water cooled reactor （SCWR） conceptual design was proposed on the basis of a mixed spectrum core concept consisting of a thermal zone and a fast zone. This new core design was considered to be the hybrid of the existing thermal SCWR and fast SCWR cores. It combines the merits of both thermal and fast SCWR cores, at the same time minimizes their shortcomings. For the thermal zone, the difficulties in the mechanical design and the maximum cladding temperature can be reduced as far as possible by the co-current flow mode; and for the fast zone, a sufficiently large negative coolant void reactivity coefficient and breeding ratio can be achieved by the big value of the ratio p/d and the multi-layer arrangement of fuel rods. The performance, including the burn-up behavior, of the proposed core was investigated with 3-D coupled neutron-physical and thermal-hydraulic calculations. During the coupling procedure, the thermal-hydraulic behavior was analyzed using a sub-channel analysis code and the neutron-physical performance was computed with a 3-D diffusion code. The results obtained so far show that the mixed spectrum SCWR concept (SCWR-M) is feasible and promising.