Based on the detailed experimental record and the statistical analysis of the data, we wish to put forward our concept on the micronuclei formation as follows: After irradiation the micronuclei were visible in the lymphocyte, their size is 1/3~1/2 of the main nuclei. The micronuclei were not derived solely from the fractions of the chromosome, but from the various components of the chromosome (such as acentric rings, microbodies, acentric fragments, various chromosome-containing mitosomes etc.) by fusing at various states and conditions in the cell plasma. Factors influencing the process of fusion include the allosteric change in membrane configuration of nuclei and of the kinetic status of the cell. According to the characteristic helical structure of DNA polynucleotide chain, we believe that under irradiation the acentric fragments of the double-nuclei lymphocyte showed a tendency to fuse leading to the formation of micronuclei. The way of micronuclei formation through fusion mechanism may be one of the main probabilities.