The invention relates to the technical field of radar detection, in particular to a satellite-borne down-looking ice-penetrating synthetic aperture radar transmission path calculation method, which comprises the following steps: acquiring earth model parameters, system parameters of a satellite-borne down-looking ice-penetrating synthetic aperture radar and echo simulation parameters; the echo simulation parameters comprise an azimuth time sequence, and an antenna position sequence and an in-ice target position in a rotating geocentric coordinate system; in the south pole, the north pole or other to-be-detected areas covered by ice, taking the part above the earth surface as an air medium and the part below the earth surface as an ice medium, for each azimuth moment, solving a corresponding geocentric angle of a corresponding transmission path in the ice medium, and further respectively determining the lengths of the transmission path in the air medium and the ice medium; and the transmission path is connected with the corresponding antenna position and the in-ice target position and is located in the beam range of the transmitting antenna. According to the method, the transmission path can be determined more accurately, and technical support is provided for radar imaging, echo simulation and the like.