SLE is a heterogeneous autoimmune disease that can present clinically as relatively mild skin lesions, as joint symptoms, or even as life-threatening involvement of vital organs. Infection is one of the leading causes of morbidity and mortality in patients with SLE. A retrospective study from the Concord Hospital analyzed the causes of death of lupus patients at the Concord Hospital over the past 26 years and found that secondary infections were present in 101 of 268 patients who died, reaching 37.3%. Further analysis of the changes in the composition of causes of death revealed that in the 1980s, the most common cause of death in patients was renal involvement, while secondary infections gradually became the most common cause of death in lupus patients in the 21st century. I. Why are lupus patients more likely to become infected? Patients with lupus have a very broad spectrum of infections, with the most common infections being bacterial, followed by viral and fungal infections. Respiratory and urinary tract infections are the most common, and skin and soft tissue infections are also more common. Among them, Streptococcus pneumoniae, Escherichia coli, Staphylococcus aureus, Mycobacterium tuberculosis, herpes zoster virus, cytomegalovirus, human papillomavirus, Candida, Pneumocystis, and Cryptococcus novelis are the common pathogens. The incidence of lupus co-infection with tuberculosis varies depending on the prevalence of tuberculosis in different regions, but in general lupus patients are at higher risk of developing tuberculosis than the general population. In TB endemic areas, the prevalence of lupus patients can reach 5%. The complex relationship between lupus and infection, which is mutually reinforcing and similar to each other, makes it difficult to distinguish lupus flares from infection in some cases. Therefore, much research has been done to find biomarkers that can distinguish traditional infections from lupus flare-ups. The more traditional and commonly used markers are CRP and PCT, and they play a role in identifying bacterial infections from lupus activity, but there are still some shortcomings that limit their use, as shown in Table 1. In recent years, many new biomarkers have been tapped for the identification of lupus recurrence and infection, but there is still a long way to go before they can be applied to the clinic. III. How to prevent serious infections in lupus patients It is difficult to identify co-infections in lupus patients and tricky to treat them, so it is important to prevent lupus infections. Vaccination is a good way to prevent infection, such as pulmonary streptococcal vaccine, influenza vaccine, hepatitis B and hepatitis A vaccine are very necessary, especially for high-risk lupus patients. However, it should be noted that live vaccines are contraindicated in patients with lupus especially those on immunosuppressive drugs. Several clinical studies have shown that hydroxychloroquine reduces the risk of infection in patients with lupus, so it should be used in all patients with lupus except those with contraindications. In addition, attention should be paid to the adjustment of hormone and immunosuppressive therapy, such as minimizing the dose of hormone use by using hydroxychloroquine and vitamin D, and not using cyclophosphamide continuously. Antibiotics can be applied prophylactically when necessary. In conclusion, there are more studies on lupus co-infection, but the mechanism of the role of infection in the development of lupus is still unclear; there are no reliable and practical markers or methods for the identification of lupus recurrence and infection, especially viral and fungal infections; lupus co-infection is difficult to identify and difficult to treat, and it is important to prevent infection well.