Abstract: There is still a misconception about the general understanding of the primary radiation damage mechanism intenationally,which stems essentially from the incorrect calibration and understanding of defects in the cascade collision process. The accurate calibration and evolution analysis on defects in the cascade collision process of zirconium have been achieved by a timeaveraged atomic volume spectrum(TAVS) method. The results indicated that(a) at the end of the thermal spike stage,the cascade region was in a molten state,and the point defects occurring in the ballistic phase disappeared almost completely;(b) during the quenching,the ultra-fast crystallization occurred in the molten region,and the primary radiation damage originated from the defect trapping behavior in this process. In addition,the higher PKA energy was enabled to lead to the formation of larger molten region,and to an increase in the formation probability of sub-cascades,thus affecting the number of stable point defects.