The flow-field-caused aero-optical effect is becoming a crucial issue in hypersonic flight. The degraded imaging results can seriously affect the aircraft’s ability to capture targets. Experiments were carried out in a Mach 6-gun tunnel, and the imaging quality of a hypersonic optical dome was investigated under six different values of pressure ratio of jet. Background oriented schlieren was used to obtain the point spread functions (PSFs), which were then used to evaluate the imaging quality of the optical dome. The experimental results showed that cooling film with higher pressure will reduce the support field of the PSF and will have a more severe influence on the imaging quality.