In this paper, we propose a new virtual experiment environment for threshold voltage (VT) distribution of 3-D Gate-All-Around (GAA) NAND flash memories with a spirit of Monte-Carlo (MC) simulation. Cell variation (CV) is modeled as a random normal distribution, and physical compact model is implemented to track threshold voltage of each cells. Influence of each widening factors and width transient of VT distribution are thoroughly investigated to focus on the difference from the conventional Monte-Carlo simulation. The resulting width transient suggests that the proposed simulation utilizing the compact model is more proactive and useful in predicting the distribution width, which is a critical factor for reliability control.