There appears the double image phenomenon in a kind of medium-wave 256×256 infrared focal plane array detector imaging,and it seriously affects the image quality.The special experiment platform of IRFPA point source was introduced,and the data characteristics of the double image were analyzed.The causes of the double image were found through mechanism analysis and experiments.The mismatch of impedance and the lack of bandwidth of the test circuit lead to the formation of double image.The double image phenomenon can be eliminated by improving the performance of the test circuit.