With the population aging, the problem of comorbidity is becoming more and more serious. Comorbidities affect the life quality of patients and increase the risk of poor prognosis. However, due to limited study and evidence, clinical decision-making becomes difficult and complicated. How to assess the comorbid condition and to guide clinical practice has become an urgent problem to be solved. This review summarized the assessment tools of comorbidity and their clinical applications in order to provide a basis for the future study of comorbidity assessment and comorbid management.