 This will be a randomized, double-blind, placebo-controlled, parallel group study to evaluate the effect of linagliptin on glucose variability and glycemic control in peritoneal dialysis patients with type 2 diabetes who are inadequately controlled with premixed insulin therapy.which will be conducted in 8 diabetes centres andor nephropathy departments in China. After a 4-week run- in period, 232 participants are randomized 1:1 to either premixed insulin combined with linagliptin 5mgd group also named combined group or premixed insulin alone group also named insulin group for 12 weeks. Finally, the primary endpoint is glucose variability indicated by MAGE, secondary endpoints include HbA1c, FPG, PPG, LAGE, SDBG, PT10.0, PT3.9, 1h fasting MBG, 3h postprandial MBG, insulin dosage, hypoglycemia and body weight. 