23 cases of thrombus formation in cardiac cavity were studied. 9 were cased by extensive trauma in soft tissue, 13 by various cardiac diseases. There was no significant difference between trauma and heart disease (p > 0.05). The white thrombus formation was mainly caused by trauma and was often found in the right cardiac cavity (P < 0.001). The mixed thrombus was mainly caused by heart disease and no difference was found between in fight and left cardiac cavity (p > 0.05). The types, positions and causes of thrombus were significantly related (p < 0.001). The causes, pathologic mechanism and forensic identification of thrombus formation in cardiac cavity were discussed.