A system for predicting microsatellite instability and a construction method thereof, a terminal device and a medium are provided. Target image information, pathological specimen information and clinical data information of a user to be predicted are acquired by an acquisition module in the system for predicting microsatellite instability; a radiomics signature is generated according to the target image information, and a pathomics signature is generated according to the pathological specimen information, by a signature generation module, based on a pre-trained MSI-H/dMMR multi-omics signature model; and MSI-H/dMMR prediction results are generated according to the radiomics signature, the pathomics signature and the clinical data information, by a prediction generation module, based on a pre-trained MSI-H/dMMR prediction model.