Abstract: This paper studies the transportation of passive scalarin the turbulence with different molecular Prandtl numbers by directnumerical simulation. This paper provides sound evidence that theturbulence Prandtl number depends on molecular Prandtl number. In thelogarithm law region, the turbulence Prandtl number Pr_T varieslinearly with the reciprocal of molecular Prandtl number in Reynoldsaverage. The relationship between subgrid-scale turbulence Prandtlnumber Pr_t and molecular Prandtl number is more complicated, theminimum Pr_t occurs at Pr=1.0