Based on steady state incompressible Reynolds-averaged Navier-Stokes equation,  turbulence model,  the three-dimension airflow and concentration fields in passenger car are calculated numerically.  Regarding passengers as cubes and the exhalant CO₂ as representative contaminant respectively,  the airflow and concentration distributions are investigated in non-empty state.  The results show that existing sew supply modes make the airflow distribution homogeneous except for the ends.  Body heat and solar radiation have much influence on airflow and temperature fields.  The air distribution in occupied passenger car differs from that in empty one.  The heat flux from body heat and solar radiation produces a much big temperature gradient in occupied passenger car.  The concentration is low in gangway zone while high in seat zone with crowded passengers.  The concentration in middle section is higher than that in end section and contaminant gathers in respiratory region,  and the polluted air can´t be exchanged effectively in seat zone,  which is disadvantageous to air quality in passenger car.