Objective: Since the beginning of the COVID-19 epidemic, a large number of guidelines on diagnosis and treatment of COVID-19 have been developed, but the quality of those guidelines and the consistency of recommendations are unclear. The objective of this study is to evaluate the quality of the diagnosis and treatment guidelines on COVID-19 and analyze the consistency of the recommendations of these guidelines. Methods: We searched for guidelines on diagnosis and/or treatment of COVID-19 through PubMed, CBM, CNKI, and WanFang Data, from January 1, 2020 to August 31, 2020. In addition, we also searched official websites of the US CDC, European CDC and WHO, and some guideline collection databases. We included diagnosis and/or treatment guidelines for COVID-19, including rapid advice guidelines and interim guidelines. Two trained researchers independently extracted data and four trained researchers evaluated the quality of the guidelines using the AGREE II instruments. We extracted information on the basic characteristics of the guidelines, guideline development process, and the recommendations. We described the consistency of the direction of recommendations for treatment and diagnosis of COVID-19 across the included guidelines. Results: A total of 37 guidelines were included. Most included guidelines were assessed as low quality, with only one of the six domains of AGREE II (clarity of presentation) having a mean score above 50%. The mean scores of three domains (stakeholder involvement, the rigor of development and applicability) were all below 30%. The recommendations on diagnosis and treatment were to some extent consistent between the included guidelines. Computed tomography (CT), X-rays, lung ultrasound, RT-PCR, and routine blood tests were the most commonly recommended methods for COVID-19 diagnosis. Thirty guidelines were on the treatment of COVID-19. The recommended forms of treatment included supportive care, antiviral therapy, glucocorticoid therapy, antibiotics, immunoglobulin, extracorporeal membrane oxygenation (ECMO), convalescent plasma, and psychotherapy. Conclusions: The methodological quality of currently available diagnosis and treatment guidelines for COVID-19 is low. The diagnosis and treatment recommendations between the included guidelines are highly consistent. The main diagnostic methods for COVID-19 are RT-PCR and CT, with ultrasound as a potential diagnostic tool. As there is no effective treatment against COVID-19 yet, supportive therapy is at the moment the most important treatment option.