To analyze the relationship between triglyceride-glucose (TyG) index and left ventricular systolic function and myocardial layer-specific strain in patients with the acute coronary syndrome (ACS) complicated with diabetes mellitus (DM). Methods Seventy-six patients suspected of being diagnosed with the acute coronary syndrome who underwent coronary angiography were enrolled from the Department of Cardiology in the First Hospital of Lanzhou University between October 2020 and December 2021. According to whether the patients were complicated with diabetes, they were divided into a simple acute coronary syndrome group, an acute coronary syndrome complicated with diabetes group, and twenty-two healthy patients during the same period were selected as the control group. The TyG index was calculated based on blood test results, and a two-dimensional layer-specific speckle tracking technique was used to measure the left ventricular global longitudinal strain in the endocardial layer (GLSendo), mid-myocardial layer (GLSmid) and epicardial layer (GLSepi), Pearson correlation analysis and ridge regression analysis were used to analyze the relationship between TyG index and speckle tracking layered strain parameters, and a model was established according to the analysis results. Results Compared with the ACS alone and control groups, the TyG index was significantly increased in ACS combined with the DM group (P < 0.05). The left ventricular ejection fraction and the strain of each layer of the myocardium were significantly reduced in the ACS combined DM group, in which the global longitudinal strain value from the endocardium to the epicardium decreased gradually. Among them, GLSendo had significant differences between the ACS combined DM group and the ACS alone group (P < 0.05). The TyG index was negatively correlated with left ventricular ejection fraction and positively correlated with GLSendo, GLSmid, and GLSepi (P < 0.05). Conclusion Speckle tracking layer-specific strain technique can quantitatively assess ventricular remodelling in patients with acute coronary syndrome and diabetes, and the TyG index, as a readily available marker of insulin resistance, is correlated with it.