Based on the parent austenite orientation reconstruction method,it is aimed to reveal the origination of high angle grain boundaries(HAGBs)and its relationship with ductility of H13 steel.The orientation relationship between martensite and parent austenite of quenched H13 samples was(123.5°,9.3°,192.5°),which agreed with the Kurdumov-Sachs relationship.The variant distribution of quenched samples was dominated by close-packed plane group,and its high length fraction of V1/V2 inter-variant boundaries of calculated 62.6％was mainly contributed to HAGBs(＞45°).When the quenched H13 samples underwent the pre-tempering treatment,their density of HAGBs(＞45°)notably increased from 1.33 to 2.39 pm-1,which improved its total elongation from 8.3％to 11.5％.Compared with the quenched H13 samples,the length fraction of V1/V2 inter-variant boundaries of H13 samples with pre-tempering for 5,10 and 60 min was reduced by 6.7％,7.0％and 7.5％,respectively.During pre-tempering treatment,V1/V3&V5 variant pairs,etc.,merged V1/V2 variant pair by strain-induced grain boundary migration,which decreased the length fraction of V1/V2 inter-variant boundaries by 7.0％.The pre-tempering treatment significantly increased HAGBs(＞45°)of H13 samples by sub-grains coarsening and strain-induced grain boundary migration mechanism.