A passive millimeter-wave scanning imaging method using electro-optic modulation and photonic processing is presented. In this imaging method, the millimeter-wave signal in the radiometer is transformed to optical frequency by electro-optic modulation, and processed by photonic filter and photodetector. The principle of this millimeter-wave signal photonic processing method is described, and the relationship between component parameters and signal conversion is analyzed. The noise characteristics of this processing method are discussed. A passive millimeter-wave scanning imaging system using this photonic processing method was designed, and passive millimeter-wave images acquired using this method were first presented in China. The results show that the proposed passive millimeter-wave imaging method is effective and can obtain comparable imaging quality as that of traditional millimeter-wave radiometer imaging. This passive millimeter-wave imaging method has advantages such as large bandwidth and immunity to electromagnetic interferences.