Because of excellent infrared stealth performance and mobility, armed helicopters can break through terminal air defense systems and play a huge role in modern warfare. Taking an Apache armed helicopter as an example, an infrared radiation model is established on the basis of a fluid dynamics software. The infrared radiation characteristics of the helicopter flying at low altitude are analyzed. For the main operation wavebands of terminal infrared air defense missiles, their infrared radiation intensity values in the middle infrared waveband from 3 to 5 μm and in the long infrared waveband from 8 to 12 μm are calculated respectively. Finally, on this basis, the main threat of an armed helicopter to terminal infrared air defense is analyzed and several methods for improving the detection and anti-interference ability of armed helicopters are discussed.