In this research, we investigated the impact of Reprogram scheme on Z-interference mitigation in the threshold voltage (Vth) distribution of 3D NAND Flash Memory. Statistical Monte-Carlo Simulation was conducted to reproduce the distribution arising from multiple cells, and Incremental Step Pulse Programming (ISPP) was used. During this process, Random Telegraph Noise (RTN) and ISPP noise were applied. The results enabled us to observe the changes in the distribution reflecting reduced z-interference, which were analyzed from various perspectives. It was confirmed that the distribution width, standard deviation of read level intervals, and number of outlier cells are all decreased. Furthermore, we examined the influence of z-interference according to distribution window settings and the application of reprogram scheme.