It is proposed that the photon response non- uniformity (PRNU) factor Φ can be used to evaluate photo response non- uniformity noise, which is based on comprehensive analysis of all kinds of optical imaging sensor noise. A test method has been established, and a test platform has also been built with a doubleintegrating sphere structure. Finally, the relationship between the PRNU noise and the incident irradiance is discussed in the whole range of the output values, which has provided a powerful support for the test of other indicators and the correction of photon response non-uniformity.