The photoelectric technique for studying detonation reaction zone of high energy explosive was presented and used to investigate the reaction zone widths of JO-9159 and JB-9014 explosives. The radiation intensity history of the shock front in chloroform was recorded by using chloroform as the window materials with an instantaneous optical pyrometer. Then the reaction width was obtained by the condition of interface continuity and the phenomena of mirror deduction. The results show that there is a obvious CJ point in the reaction zone of JO-9159 explosive,but not the case for JB-9014 explosive,furthermore,the reaction zone width of JO-9159 explosive decreases with the decreasing of explosive density.