Abstract: To improve the economics of nuclear heating reactor and achieve multi-purpose targets for electric and steam supply, desalination and heating, the main thermal parameters should be greatly improved. Therefore, a new nuclear heating reactor type NHR-200Ⅱ was proposed. Compared with previous NHR-200, the thermal parameters of NHR-200Ⅱ should be greatly increased. At the same time, the characteristics of system simplified and inherent safe should be kept. To achieve this goal, the design features of nuclear heating reactor, such as integrated arrangement, full power natural circulation, self-pressurized performance and passive safety were employed. The efficiency was improved by exploiting potential and reasonably matching system parameters. The simulation results of two design extension conditions show that the passive safety system is effective and the core uncover will not occur on loss of coolant accident condition. This research can also provide reference for the design of other small water cooled reactors.