Background: This study aimed to investigate the correlation between glucose fluctuation from self-monitored blood glucose (SMBG) and the major adverse cardiac events (MACE) in diabetic patients with acute coronary syndrome (ACS) during a 6-month follow-up period using the WeChat application. Methods: From November 2016 to June 2017, 262 patients with ACS were discharged in a stable condition and completed a 6-month follow-up period. SMBG was recorded using the WeChat application. The patients were divided to a high glucose fluctuation group (H group; n = 92) and a low glucose fluctuation group (L group; n = 170). The 6-month incidence of MACE, lost-to-follow-up rate and satisfaction rate were measured through the WeChat follow-up. Results: MACE occurred in 17.4% of patients in the H group and in 8.2% of patients in the L group (p = 0.04). Multivariable analysis suggested that high glucose fluctuation conferred an 87% risk increment of MACE in the 6-month follow-up period (odds ratio: 2.1, 95% confidence interval 1.95-4.85; p = 0.03). The lost-to-follow-up rate was lower and the satisfaction rate was higher in the patients using the WeChat application during follow-up than those of the regular outpatient follow-up during the same period (p < 0.05). Conclusions: The trial demonstrates that higher glucose fluctuation from SMBG after discharge was correlated with a higher incidence of MACE in diabetic patients with ACS. WeChat follow-up might have the potential to promote a good physician-patient relationship.