Abstract: The flow and heat transfer characteristics of a complex turbine cooling system were numerically simulated,which was a multi-cavity,multi-inlet and multi-outlet system installed in a typical small turbofan engine.The cooling system includes the cavity behind the high pressure turbine disc,the cavity in front of the low pressure turbine disc,supporting guide vane cavity,bearing cavity,and some connecting cooling air passages.In this study,the computational grids in both fluid domain and solid domain were established together,the heat transfer between the two domains was calculated conjointly.Based on the results,the influence of structural parameters and pneumatic parameters on the temperature distribution of the system,especially for the bearing cavity,was analysed,and then some measures were taken to lower down the temperature of beating cavity.This study shows the potential power of numerical simulation of fluid flow and heat transfer in complex flow system,helping to improve system design.