A method and a system for detecting geological structure of an extraterrestrial solid planet by using a single-transmitter and multiple-receiver (STMR) radar are provided. The method comprises obtaining the detection of thickness distribution and geological structure of each geological layer on the extraterrestrial solid planet by using a STMR mode, and calculating information of the dielectric coefficients and the depth of the respective geological layer. There are two detection channels having different depths of detection and detection resolutions, in which a first channel operates in a HF/VHF band for detecting geological structure of rocks on the extraterrestrial solid planet, and a second channel operates in a UHF band for detecting geological structure of regolith on the extraterrestrial solid planet. These two detection channels can cooperate with each other, ensuring accuracy and reliability of the detection.