[en] RELAP5 - a thermal hydraulic system code - in recent years is used by many researchers in Vietnam for the reactor thermal-hydraulic analysis. In the other hand, VVER-1000 reactor is selected to be the nuclear reactor technology for the first nuclear power plant in Vietnam. So the studying on VVER-1000 reactor is very important. The project purpose is modeling the thermal-hydraulic systems of VVER-1000 reactor. The project also targets enhancement of experiences in using RELAP5/SCDAPSIM code and modeling for components of VVER-1000 reactor in steady state and transient, including: steady state at 100% power, transient with switch off 1 or 2 main coolant pumps. The thermal hydraulic parameters were analysed versus time. The thermal hydraulic parameters, such as: outlet pressure, coolant temperature, maximum fuel temperature, water level of pressurizer and steam generator, etc. were compared, analysed and assessed. In steady state, the errors are less 10 per cent. (author)