Objective:To investigate the relationship between the E2 and E4 alleles of apolipoprotein E (apoE) gene and myocardial infarction (MI) in type 2 diabetes Mellitus (T2DM) patients, and to explore the relationship between apoE polymorphism and blood lipid metabolism.Methods:This case control study was conducted from August 2016 to March 2020 in China-Japan Friendship Hospital, 3 459 inpatients with T2DM were included including 3 044 patients without MI (T2DM group) and 415 patients with MI (T2DM+MI group). Real time fluorescent quantitative PCR was used to detect apoE polymorphism. Automatic biochemical analyzer was used to detect lipid levels. Logistic regression analyses were performed to determine the association of apoE with risk of MI in patients with T2DM.Results:(1) The frequency of E4 allele in T2DM+MI group (12.29%, 102/830) was significantly higher than in T2DM group (9.13%,556/6 088), while the frequency of E2 allele in T2DM+MI group (7.35%,61/830) was significantly lower than that in T2DM group (8.21%,500/6 088), P=0.012. Logistic regression analyses showed that E4 allele carrier (E3/E4+E4/E4) faced a higher risk for MI in T2DM patients ( OR=1.48, 95% CI 1.14-1.92, P=0.003), while E2 allele carrier(E2/E3+E2/E2)did not face a higher risk of MI in T2DM patients ( OR=0.88, P=0.642). (2) The levels of apoE polymorphism and blood lipid: The levels of TC, LDL-C and apoB increased in the order of E4 allele, wild type and E2 allele ( P<0.05). The levels of HDL-C, apoA1 and apoE decreased in the order of E4 allele, Wild type and E2 allele ( P<0.05). Conclusion:The E4 allele is a risk factor for MI in T2DM patients, and apoE polymorphism can affect blood lipid level in this patent cohort.