This experiment was conducted to study the influence of hyperinsulinemic and euglycemic simultaneous infusion on milk fat synthesis in lactating goats. In the experiment, four mid-late lactation  Wendeng goats with temporary carotid, jugular vein, and mammary vein catheters were assigned to a 2×2 cross over experiment of 2 treatments including control and hyperinsulinemic and euglycemic simultaneous infusion treatment. The experiment consisted of 2 periods with each of 10 d, and there was an interval of 5 d between the 2 periods. The first five days in each period was for the baseline measurements, while the second five days for the hyperinsulinemic and euglycemic simultaneous infusion. During the experiment, insulin and glucose were injected continuously (24 h/d). The rate of insulin injection through jugular vein catheter was 1 μg/ h·kg BW, while that of glucose injection was adjusted on the basis that blood glucose (25% w/v) concentration was kept within  ±20% of the base level. Daily mixed concentrate was equally divided into 12 parts and delivered by the automatic feeder every two hours, and water was free to drink during the experiment. The study results showed that the hyperinsulinemic and euglycemic treatment significantly increased the plasma insulin concentration, and there was no significant difference in the blood glucose concentration from the control group, realizing the expected treatment effects. Both milk fat content and yield significantly decreased in infusion goats (P<0.05), and there was no significant effect on other milk components (P>0.05). Hyperinsulinemic and euglycemic simultaneous infusion treatment significantly decreased the TG, acetic acid and NEFA concentration  (P<0.05) and the rate and speed of the mammary tissue’s absorption of NEFA, while significantly increased the speed of its absorption of acetic acid. Milk fatty acid compositions have been modified by infusion treatment. Contents of C12∶0 , C14∶0 and C16 in milk fat increased（P<0.05）, while that of C18∶0 and transC18∶1 decreased, but there was no effect on trans -10,cis-12CLA. Contents of total medium chain fatty acids (C10～16) and total long chain fatty acids  (≥C18) in milk fat was not affected by the infusion treatment, but that of short chain fatty acids (C4～8) showed a significant decrease (P<0.05). As shown in the results of this study, insulin may lead to the decrease in milk fat by decreasing the availability of absorbed fatty acid for milk fat synthesis in mid late lactating goats.