A computer-simulation-based approach has been proposed to estimate fundamental human error probability (HEP) parameters, which are required for Human Reliability Analysis (HRA) as related with Probabilistic Safety Assessment (PSA) foe nuclear power plant (NPP). The HEP parameters are represented by time versus reliability correlation (TRC) which is called as ¡ÇTime versus Cognitive Reliability¡Ç (TCR) curves. In the developed simulation system, ¡Çhuman model adjustment factors¡Ç were proposed to model the inherent variety and diversity in human cognitive behaviors, which are considered as the primary factors that generate different TCR. Inter-comparisons were also made between the TRC curves obtained from a laboratory experiment and the ones by the developed simulation system. It turns out that both TCR curves agree well with each other and it suggests that the computer simulation approach would be a promosing technique for estimating HEP.