traet：The air leaked—in diffuser is a key equipment of the attitude simulation test of a kind
of rocket engine．The internal flow field is an important basis for the diffuser performance assess—
ment．Three kinds of diffuser models with different air clearances(0mm，10mm，20mm)were ana—
lyzed and computed based on the Computational Fluid Dynamics(CFD)software，and the pressure
parameters distribution and the temperature parameters distribution of the internal flow fields of the
diffuser at different clearances were obtained．Tests show that the computational fluid dynamics analvzing
results of the diffuser flow field are in good accordance with those of the tests，the diffuser
model is correct．The influence of nozzle off—center on the diffuser flow field is alSO studied．