Purpose The objective of this study was to assess the accuracy of FreeStyle Libre Pro (FSL-Pro) flash continuous glucose monitoring (CGM) in patients with type 2 diabetes mellitus (T2DM) and acute myocardial infarction (AMI). Methods A single-arm, single-center prospective study was conducted in the cardiac care unit from January 2021 to September 2023. Patients underwent finger-prick blood glucose (FPBG) testing before breakfast (6:00 am) and after meals (at 9:00, 13:00, 19:00 pm), along with CGM during their hospitalization. Statistical analyses included mean differences (MDs), mean absolute relative difference (MARDs) of blood glucose levels, and hypoglycemia occurrences. A Bland–Altman plot analysis and Pearson correlation were performed. Results Ninety-seven T2DM and AMI patients underwent CGM for up to 72 h (1142 monitoring point). Mean daily BG, Fasting plasma glucose (FPG) and mean postprandial plasma glucose (PPG) were significantly lower by CGM than by FPBG with an estimated MD of −0.89 mmol/L in BG, −0.88 mmol/L in FPG, and −0.90 mmol/L in PPG, respectively. The maximum effect was mainly in the first day and then the difference was gradually declined (falling range, Day1, −1.24; Day 2, −0.70; Day 3, −0.68, mmol/L, respectively). The incidence rates of hypoglycemia and potential hypoglycemia was 1.57% and 8.5% higher, respectively, in CGM than in FBPG. A Bland–Altman Plot revealed some variability and bias between the two methods of measurement of glucose monitoring ( p < .001). Pearson's correlation coefficient demonstrated a significant correlation between the mean BG, FPG, and PPG of CGM and FBPG (Pearson's coefficient: 0.92, 0.87, 0.92, respectively, p < .001). Conclusion Compared with FPBG, FSL Pro-CGM showed lower mean glucose and higher hypoglycemia detection in T2DM and AMI patients, especially in the first 24 h.