Objective:To analyze the changes of serum 25-hydroxyvitamin D 3[25-(OH)D 3] expression in diabetic patients and its correlation with macrovascular complications. Methods:Two hundreddiabetic patients admitted to Cangzhou Central Hospital from February 2018 to November 2019 were divided into macrovascular complications group (87 cases) and without macrovascular complicationsgroup (113 cases). According to the degree of 25-(OH)D 3 deficiency, 32 cases were divided into 25-(OH)D 3 normal group, 94 cases were mild deficiency group and 74 cases were moderate and severe deficiency group. At the same time, 168 outpatients were selected as control group. The levels of serum 25-(OH)D 3 were compared between diabetic group and control group, macrovascular complications group and without macrovascular complications group, and the correlation between the level of serum 25-(OH)D 3 and carotid intima-media thickness (IMT) was analyzed. Results:The level of serum 25-(OH)D 3 in diabetic group was lower than that in control group: (24.79 ± 3.02) μg/L vs. (39.18 ± 4.38) μg/L, the difference was statistically significant ( P<0.05). The level ofserum 25-(OH)D 3 in diabetic patients with macrovascular complications group was lower than that in without macrovascular complications group: (21.08 ± 2.64) μg/L vs. (27.65 ± 3.31) μg/L; while the IMT was higher than that without macrovascular complications group: (1.29 ± 0.13) mm vs. (0.93 ± 0.10) mm, the differences were statistically significant ( P<0.05). The incidence of macrovascular complications in 25-(OH)D 3 moderate and severe deficiency group was higher than that in 25-(OH)D 3 mild deficiency group and 25-(OH)D 3 normal group: 60.81%(45/74) vs. 40.43%(38/94), 12.50%(4/32), the difference was statistically significant ( χ2 = 21.896, P<0.05). The level of serum 25-(OH)D 3 in patients with diabetic macrovascular complications was negatively correlated with IMT ( r = -0.513, P<0.05). Conclusions:The level of serum 25-(OH)D 3 in diabetic patients is decreased, and the change of its concentration is related to the occurrence of macrovascular complications.