This article analyzes the epidemic situation in all provinces of China, considering the impact of population mobility in all provinces during the Spring Festival transportation without restricting people's free movement in Wuhan. According to the characteristics of novel Coronavirus, we choose the SEIR model to establish the required differential equations. On this basis, we establish different differential equations according to the characteristics of Wuhan and all provinces of China. By collecting relevant data and using particle swarm optimization algorithm for data fitting, we predict the epidemic situation of domestic provinces during the period from the first case to March $1^{\mathrm{s}\mathrm{t}}$ while Wuhan is not sealed off, which reflects the necessity of Wuhan sealed off.