Objective To observe the changes of the formation time of venous thrombus in rats, and to provide new ideas and methods for the estimation on thrombus formation time of the forensic cases died from thrombosis. Methods Totally 80 rats were randomly divided into 10 groups （0 h, 3 h, 6 h, 12 h, 1 d, 3 d, 1 week, 2 weeks, 3 weeks and 4 weeks after operation）. A vein thrombosis model was established by the “narrow” method. The processes of thrombosis, organization, recanalization and the features of change on hemosiderin and calcium salt were observed by HE stain, Perls stain and Von Kossa stain. The expression changes of CD61, α-SMA and CD34 were observed by immunohistochemical staining technique. Results Platelets adhered to the exposed blood vessel intima 3 h after operation, and platelet trabeculae were formed by the repeated accumulation of platelets 1 d after operation. The thrombus organization formed through the fibroblasts from vessel wall that grew into the interior of the thrombus 3 d after operation. Endothelial cells covered the surface of thrombus and then the new blood vessels were reformed, and the vessels were reconstructed. The expression of CD61 upregulated at the stages of the thrombus formation （3 h） and thrombus reformation （4 weeks）, and reached the peak 1 d after thrombus formation. The release of hemosiderin and the initial expression of α-SMA were detected 3 d later. Calcium deposit and expression of CD34 were observed 1 week later. Conclusion The hemosiderin, calcium salt, CD61, α-SMA and CD34 show time-dependent changing characteristics, which is expected to provide a reference for the estimation on thrombus formation time of the forensic cases died from thrombosis.