This manuscript found out the main problems and potential risks in medical insurance and medical assistance by sorting out the emergency measures for medical insurance and medical assistance during the outbreak of COVID?19. The study analyzed the characteristics of the epidemic risk， and their special requirements of the system normalization， fairness， public character， and positive externality of medical insurance so as to improve the medical insurance and medical assistance mechanisms for major diseases. This study further analyzed the reform and improvement on seven aspects， including the fund?raising， object confirmation， fee payment， service provision， fee settlement， guarantee coordination and the supplementary security mechanism， which provided countermeasures and suggestions for improving the medical insurance and medical assistance systems of major diseases， and provided reference for improving the modernization level of the medical security governance system and governance capacity.