We simulate the B, As and P implantations into HfO2 from 3keV to 40keV by a simulator LEACS developed based on molecular dynamics method and by the traditional Monte Carlo simulator TSUPREM4 respectively. The LEACS results accurately fit with the SIMS (secondary ion mass spectroscopy) data, while the TSUPREM4 results deviate from the SIMS data obviously except B implantation. Based on the verification of the simulator, influence of the oxide thickness on the retained range profiles in the Si layer has been quantitatively investigatedin the case of HfO2/Si and SiO2/Si structures. The range profiles in the Si layer through HfO2 shift to the surface obviously for about 0.68 times of the oxide layer thickness on the average in comparison to those through SiO2. It can be predicted that this effect will have a significant impact on MOSFET (metallic oxide semiconductor field effect transistor) device performance in the integrated circuit process of the next decade if HfO2 is used to replace SiO2 as the gate dielectric.