TiC-doped 12-filament MgB2 wires was prepared by PIT method and enhanced by Cu/Nb composite cores. The precursor powder was treated in two steps. The effects of different temperatures on the phase composition, microstructure and superconductivity of the MgB2 wires were studied. Results show that two-step powders can increase the C substitution level effectively, and meanwhile the grain size of MgB2 reaches submicrometer level in the cores. MgB2 grains have good bonding property. The Jc can reach 3×104 A/cm2 when the wires are prepared at 4.2 K, 5 T.