Objectives To detect expressions of heat shock protein 70 (HSP70) and glial fibrillary acidic protein (GFAP) , and to estimate the post-injury interval after concussion of brain via the ratios of percentage of HSP70/GFAP-positive cells. Methods We established a brain concussion model of rat. Tissue levels of HSP70 and GFAP were determined by immunohistochemical staining at different time points after injury. Finally, the relationship between the ratio of percentage of HSP70/GFAP-positive cells and the post-injury interval was measured. Results The ratio of percentage of positive cells (increased from 7.15 to 11.73) and the percentage of HSP70-positive cells (P<0.05, compared with control group) increased, and the percentage of GFAP-positive cells did not change remarkably (P<0.05, compared with control group); the post-injury interval was between 0.5 hour and 3 hours. High ratio (>6.66) and high percentage of HSP70 and GFAP-positive cells (P<0.05, compared with control group) indicated the post-injury interval was between 3 and 12 hours. A low ratio (<6.66) and high percentage of HSP70 and GFAP-positive cells (P<0.05, compared with control group) suggested that the post-injury interval was later than 12 hours. Conclusion By analyzing the variation rule of the ratio of percentage positive cells after brain concussion, the post-injury interval after concussion of brain could be estimated.