【Abstract】Objective To investigate the effect and mechanism of DEX on oxidative stress and apoptosis induced by high glucose in cardiomyocytes. Methods The cardiomyocyte H9C2 was cultured in vitro, and a high glucose injury model was established. The cardiomyocytes were treated with DEX with different concentrations (5 μg/L, 10 μg/L, 20 μg/L),respectively,which were recorded as experiment 1 group, experiment 2 group, experiment 3 group. The contents of LDH, MDA and SOD were detected. qRTPCR was used to detect the expression of miR126. miRNC, miR126 mimcis, antimiRNC, and antimiR126 were transfected into cardiomyocytes, respectively, with DMEM medium containing 35 mmol/L glucose and 20 μg/L DEX to cultivate. Flow cytometry was used to detect the apoptosis rate. Western blot was used to detect the expression of procaspase3 and clcaspase3. Results Compared with the control group, the levels of LDH and MDA in the high glucose injury model group were significantly increased (P＜0.05), the content of SOD was significantly reduced (P＜005), the expression level of miR126 was significantly reduced (P＜005), and the apoptosis rate was significantly increased (P＜005), the level of clcaspase3 protein was significantly increased (P＜005), and the level of procaspase3 protein was significantly decreased (P＜005). Compared with the high glucose injury model group, the contents of LDH and MDA in experimental group 1, experimental group 2 and experimental group 3 were significantly reduced (P＜005), the content of SOD was significantly increased (P＜005), and the expression level of miR126 was increased (P＜005), the apoptosis rate was significantly reduced (P＜005), the level of clcaspase3 protein was significantly reduced (P＜005), and the level of procaspase3 protein was significantly increased (P＜005). There was a statistically significant difference in each index among the experimental group 1, the experimental group 2, and the experimental group 3 (P＜005). Compared with miRNC group, the content of LDH and MDA in miR126 group was significantly reduced (P＜005), the content of SOD was significantly increased (P＜005), and the apoptosis rate was significantly reduced (P＜005), the level of caspase3 protein was significantly reduced (P＜005), and the level of procaspase3 protein was significantly increased (P＜005). Overexpression of miR126 could enhance the effect of DEX on high glucoseinduced oxidative stress and apoptosis in myocardial cells, and inhibition of miR126 expression could attenuate the effect of DEX on high glucoseinduced oxidative stress and apoptosis in cardiac muscle cells. Conclusion DEX could inhibit the oxidative stress and apoptosis of cardiomyocytes induced by high glucose by upregulating the expression of miR126.