As a small multi-purpose modular pressurized water reactor,ACP100 is a landmark achievement of China's independent research and development.This paper introduces the research and development process,the main characteristics of the reactor core and safety design technology,mainly including the reactor core design,thermal-hydraulic design,safety design concept,inherent safety design,and the strategy for accident response.Through the introduction of the fully passive safety design concept,and combination of the deterministic theory and probabilistic theory,the safety of ACP100 fully meet and beyond the safety standards of Gen.III nuclear power plant.