Objective To investigate the correlation between the early phase insulin secretion index and 72 h continuous glucose levels in patients of impaired glucose tolerance (IGT). Methods According to repeated 75 g oral glucose tolerance test (75 g OGTT) ,62 cases were divided into 2 groups: normal glucose tolerance group (NGT group, 30 cases) and isolated impaired glucose tolerance group (IGT group, 32 cases). Insulin levels were detected and HOMA-IR,HOMA-β , ΔI30/ΔG30,AUCI were calculated. The blood glucose levels were monitored by continuous glucose monitoring system for 72 h. The characteristics of postprandial glucose excursion were studied based on peak postprandial glucose (PPC) concentration, time to PPG (Δt) , postprandial glucose excursion (PPGE) and duration of postprandial glucose excursion (DPE). They were statistically analyzed by SPSS12.0. Results The levels of PPG and PPGE were significantly higher in IGT group (P < 0.05). Δt and DPE delayed obviously in IGT group (P < 0.05). HOM A-IR in IGT group was higher than that in NGT group (1.68 ± 1.03 vs 1.15 ± 0.90, P < 0.01), Δ I30/ΔG30 and HOMA- β was significantly lower in IGT group than that in NGT group (3.85 ± 1.04 vs 6.42 ±1.05,52.97 ± 2.02 vs 55.68 ± 12.45, P < 0.01 or < 0.05). Conclusions Higher postprandial glucose levels are characteristics of IGT patients,and the function of islet β cell after glucose load is impaired more severely. The levels of FPG and 2hPG are positively correlated with insulin resistance, and negatively correlated with islet β cell function.