Abstract: Objective To investigate the reason for the appearance of bimodal insulin release curve (IRC).Methods Sixty-three cases of bimodal pattern of IRC (double hump group) were selected as experimental group; 18 normal volunteers as control group. Oral glucose tolerance test, insulin release test and C-peptide release test were performed, and the index of steady-state model was calculated.Results There were no significant difference among the two groups in fasting insulin, 1 hC-peptide, fasting plasma glucose, Homa-insulin resistance. 0.5 hIns:double hump group > control group. Fasting C-peptide:control 1 group > double hump group > normal Group. 0.5 h C-peptide:double hump group and control group > normal group. Fasting plasma glucose:normal group > double hump group and control group. 0.5 h plasma gulcose:normal group > double hump group > control group. glucose area under curve:normal group > double hump group > control group; △I₃₀△ G₃₀:double hump group > control group > normal group. insulin area under curve and C-peptide area under curve:double hump group > control group and normal group.There were significant difference among the results.Conclusion s The pancreatic island has an overcompensation in the first secretion phase in double hump group, and the insulin displayed the pseudopeak value at 0.5 h which lead to the increase of blood glucose. The pancreatic island has a normal peak value in the second secretion phase, the patients in this group exsits impaired glucose tolerance.