Covid-19 has spread all over the world. It not only makes lots of people die but also has a huge negative impact on the economy in the world. In order to resist the Covid-19, many researchers have applied machine learning algorithms to deal with different problems brought by Covid-19. No one has summarized different machine learning algorithms and their applications to the Covid-19. Thus, in order to help people understand the importance of machine learning algorithm in the medical field and principles of some machine learning algorithms. We write this review that covers three different machine learning algorithms, which are Artificial neural network (ANN), Fuzzy neural network (FNN) and Convolutional neural network (CNN), and their applications to the Covid-19 and related fields. In the end, we found that different machine learning algorithms with different merits can be used to deal with many Covid-19 problems such as predicting Covid-19 incidence rate, vaccine design and the diagnosis of Covid-19. To some extend, this review can help researchers find solutions when they met similar virus-related problems.