Under the large uncertainty and unknown condition all over the world, a growing number of people are developing mental illnesses after COVID-19. Anxiety, major depression disorder, eating disorder, and Post-traumatic stress disorder, all of these mental disorders are collected for the majority of mental illnesses after COVID-19. The primary aim of this paper was to determine the prevalence, causes, effects, and treatments among mental illness patients after COVID-19. By reviewing the paper that has been published, it is nearly certain that psychological disorders will occur after suffering traumatic events and the outbreak of COVID-19, which is seen as one of the most serious pandemics in the world in the last few decades, a number of populations are undergoing a high level of psychological illness. Eye Movement Desensitization and Reprocessing therapy can be one of the great therapies to treat mental illnesses after COVID-19. According to a study, Eye Movement Desensitization and Reprocessing treatment can greatly affect traumatic memories for psychological patients. After COVID-19, a growing number of populations become infected with mental disorders, therefore, the causes and some effective treatments are required. Especially those who have a previous history of psychological disorders might need some specialized intervention.