When an aircraft flies at a hypersonic speed within the atmosphere, the temperature of the infrared window (IRW) on the aircraft will rise rapidly due to the high-speed incoming flow will produce a severe aerodynamic heating to its optical detection window. The infrared (IR) radiation of the high-temperature gas and optical window will generate severe pneumatic thermal radiation effect upon the detection system, with the performance of the IR detector possibly being reduced or even destroyed. <p> </p>To evaluate the influence on the target imaging made by the IRW radiation, the experiment on the basis of building a simulating model is conducted by the means of ray tracing so that the accurate transmittance of the IRW can be observed under the different temperature. And then the radiation distribution of the thermal radiation on the detector generated by the IRW radiation noise and target signal can finally be obtained. <p> </p>This paper also records the different parameters in the detection system being set in the experiment, and analyzes the different influences brought by various factors to the Signal to Noise Ratio (SNR). It is also expected that it will provide a data reference to the following research of radiation noise suppression and design of IR detection system.