Objective To explore the cognition on diabetes and insulin of the patients with type 2 diabetes mellitus (T2DM). Methods We recruited 130 T2DM inpatients on insulin therapy who met our inclusion criteria. All patients finished the questionnaire surveys for related knowledge of diabetes and insulin upon admission and after receiving one-week targeted health education in hospital. Results (1) The average levels of hemoglobin A_1c (HbA_1c), fasting blood glucose (FBG) and 2-hour postprandial blood glucose (2-hPBG) were (9.82±2.37)%, (7.39±2.07) mmol/L and (10.29±3.22) mmol/L, respectively, and the standard-reaching rates were 10.00%, 53.85% and 55.38%, respectively. (2) Lack of basic knowledge of diabetes. Patients' cognition rates of target glycemic levels and frequency of glucose monitoring were low. For blood glucose control standards and monitoring frequency, the cognition rate of the patients after admission was higher than that of the patients on admission (P <0.05, P <0.01). (3) Cognitive misunderstanding on insulin. Compared to those with insulin therapy at admission, the patients who were about to receive insulin showed more anxiety about insulin usage (some P <0.05). The concerns about the use of insulin were decreased in both groups after admission (some P <0.05). (4) Awareness of disease monitoring was to be emphasized. Compared with those were to use insulin on admission, the patients with insulin therapy had better awareness of disease monitoring (P <0.05, P <0.01). The cognitive rates on disease monitoring were significantly increased in both groups after admission (some P <0.01). (5) There were great concerns about insulin therapy. They were afraid of many things including "addicted to insulin" and "fault in injecting insulin". Conclusion The blood glucose control status of T2DM patients with insulin therapy or being about to insulin therapy is poor. T2DM patients lack the related knowledge on diabetes and insulin, which is an important factor affecting insulin therapy and glucose management. Individualized T2DM education is needed to improve the situation.