Abstract: The microstructure evolution induced by irradiation on materials will lead to dimensional instability and mechanical property degradation of structure materials, which is one of the major factors to limit the safety and economical feature of nuclear plants. In this work, a physical model and numerical code named Radieff were developed based on rate theory, and the subsequently molecular dynamics (MD) method was used to calculate the input parameters of the model, such as formation energy, binding energy, migration energy and the stable configuration of interstitial loops. Finally, the interstitial loop evolutions in high purity iron by 1 MeV electron irradiation were reproduced with the model and code, and calibrated by experiment results. According to the MD results, it is found that the stable configuration is 〈110〉 direction for 3 self-interstitial atoms (SIAs) cluster, then turn to 〈111〉 direction for larger cluster. The effects of dislocation density on the evolution of interstitial loops induced by electron irradiation were studied by Radieff under the temperature of 400-600 K and the dose rate of 1.5×10^-4 dpa/s. The effect of dislocation density on number density and size of interstitial loops depends on the comparison of the sink strengths between dislocation and interstitial clusters to SIAs. Under the radiation temperatures of 464 K and 550 K, the number density and size of interstitial loops decrease rapidly when the dislocation density gets to 10¹¹ cm^-2 and 10¹⁰ cm^-2 respectively, as a result of lager sink strengths of dislocation than interstitial clusters to SIAs.