Advanced thermal hydraulic simulation of nuclear reactors is introduced using the CUPID code, which is a 3-dimension 2-phase flow analysis code developed by the lecturer when he worked for Korea Atomic Energy Research Institute (KAERI). Mathematical and physical models adopted in CUPID will be presented. Then, the application of CUPID for nuclear thermal hydraulic analysis will be introduced. Wide range of applications will be discussed from the CFD-scale analysis to resolve local phenomena to a safety analysis for the whole reactor coolant system. Multi-scale and multi-physics analysis methods are applied for the high-resolution safety analysis using CUPID. The concept of multi-scale and multi-physics analysis will be explained with their applications.