Up to August 19, 2021, there have been 207,784,507 confirmed cases and 4,370,424 confirmed deaths worldwide because of the COVID-19. Facing such a difficult situation of the epidemic situation of COVID-19, all the countries must struggle together and help each other. Just as the Peterson Institute for International Economics says in their report: The pandemic is not under control anywhere unless controlled everywhere. Therefore, it is crucial to pay more attention to the developing countries with fewer vaccines of COVID-19 and insufficient medical resources. Considering that India is one of the largest developing countries and the epidemic situation there is very serious, we decided to choose India as our research object. We propose a modified SEIR model, added the vaccination rate and the stringency of isolation measures - two crucial factors of the development of the COVID-19. It can be a helpful reference to comparative research and policies of governments and help us better judge the epidemic situation in developing countries.