Objective To determine 1 hour plasma glucose cutoff value during OGTT to screen diabetes and IGR and its relationship with islet β cell function and insulin sensitivity. Methods 4731 subjects were recruited to perform an OGTT.The cutoff value of 1h-plasma glucose during OGTT was analyzed by receiver operating characteristic curve (ROC curve).And according to the two cutoff values,we classified all the subjects to three groups,and compared HOMA-IR,HOMA-β,insulinogenic index and shape index among groups,then analyzed its correlation with each parameter. Results According to ROC results, to diagnose type 2 diabetes mellitus,the optimal cutoff value of 1h plasma glucose during OGTT was 12.935mmol/L,with sensitivity of 81.52%,specificity of 86.94%. To diagnose impaired glucose regulation(IGR),the optimal cutoff value of 1h plasma glucose was 9.815mmol/L,with sensitivity of 74.96% and specificity of 77.86%. We classified all the subjects to three groups, and among the three groups the insulinogenic index, shape index, HOMA-IR, HOMA-β showed statistically significant difference (all P＜0.01). There was a negative correlation of OGTT-1hPG with insulinogenic index and HOMA-β(all P＜0.01) and a positive correlation of OGTT-1h PG with shape index and HOMA-IR (all P＜0.01). Conclusions To diagnose type 2 diabetes mellitus,the optimal cutoff value of 1h plasma glucose during OGTT is 12.935mmol/L.To diagnose impaired glucose regulation(IGR),the optimal cutoff value of 1h plasma glucose is 9.815mmol/L.And 1h PG can reflect the islet β-cell function and insulin resistance.