The outbreak of 2019 novel coronavirus disease (COVID-19) has become a public health emergency of international concern. The purpose of this study was to propose an improved dynamic SEIR (ID-SEIR) model to predict the epidemic trends of novel COVID-19. Firstly, we obtain the values of parameters in ID-SEIR model by using the epidemic data of Wuhan as the training sample. Secondly, we predict the epidemic trends of COVID-19 for the three most serious USA, New York and Italy with our proposed ID-SEIR model, and we can apply the proposed method to predict the epidemic trends of other countries and areas. Finally, we find that the proposed ID-SEIR model established in this paper has strong reliability, which can reasonably reflect the changes in national policies and public behavior during the epidemic. Also, this model can make predictions in line with the actual development of the epidemic and provide reference for infection prevention and control.