The invention discloses an amplitude phase characteristic test method for a down-conversion reception channel of an ultra-wide band synthetic aperture radar (SAR) receiver and relates to an SAR system testing technology. The amplitude phase characteristic test method comprises a first step of establishing a parametric mixer and connecting a vector network analyzer; a second step of performing standard single-port correction on two ports of the vector network analyzer respectively within an input frequency range and an output frequency range of the tested down-conversion reception channel; a third step of establishing a calibration mixer and performing representation of the calibration mixer; a fourth step of utilizing the calibration mixer to perform straight-through calibration; and a fifth step of testing amplitude phase characteristics of the down-conversion reception channel. The method is mainly used for measuring amplitude phase frequency characteristics of the down-conversion reception channel of the synthetic aperture radar multichannel receiver and has the advantages of being high in measuring precision and simple, convenient and fast to achieve, and necessary means are provided for accurate extraction and compensation of SAR system amplitude phase errors.