Abstract: The multi-beam reflector antenna is the front-end receiver of the passive imaging system. Due to spatial coherence effect of electromagnetic field, the uniform multi-beam parabolic reflector antenna is analyzed. The calculated results show that the beam generated by a multi-feeds parabolic reflector antenna is a coherent beam not a multi-beam when the distance of feeds reduced. It is proved that the effect of spatial coherence will reduce, the independent beam will arise when the distance of feeds is increased. The analysis is validated by FEKO soft.