Formation and evolution of interstitial dislocation loop induced by radiation damage in a material are confirmed to seriously affect the performance of the material under irradiation. For example, in body-centered cubic Fe based alloy, 1/2 $\left\langle 111 \right\rangle $ and $\left\langle 100 \right\rangle $ are mainly formed during the irradiation, which is related to various degradations of material properties. Thus, the understanding of their effect on radiation damages of material is always one of the hottest topics in nuclear material society. Previous studies have shown the surface effect on 1/2 $\left\langle 111 \right\rangle $ loop through the investigation of the interaction between 1/2 $\left\langle 111 \right\rangle $ loop and {111} surface. Considering the difference in property between 1/2 $\left\langle 111 \right\rangle $ loop and $\left\langle 100 \right\rangle $ loop, in this work the interaction between a $\left\langle 100 \right\rangle $ loop and {100} surface is studied in detail through the molecular dynamics method. The simulation results indicate that the factors including Burgers vector of loop, loop-to-surface depth, interaction between pre-existing $\left\langle 100 \right\rangle $ loops, and temperature, all seriously affect the interaction between loop and surface. Especially, the present results show for the first time the evolution of Burgers vector of $\left\langle 100 \right\rangle $ loop from $\left\langle 100 \right\rangle $ to 1/2 $\left\langle 111 \right\rangle $ and its one-dimensional diffusion to surface. According to these results, we also further explore the surface evolution after its interaction with loop. The appearance of atomic island results in the rugged surface morphology. All these results provide a new insight into the radiation damage to the surface of material.