Abstract: For the insulin therapy of diabetes, an semi-continuous dynamical system with three physiological time delays and state feedback impulsive insulin injection is proposed. A strict mathematical definition of the solution of general delay semi-continuous dynamical system is firstly given. Then the permanence of the glucose concentration in the model is discussed. Besides, numerical analyses show that the reasonable defined control level can maintain the glucose concentration in the range that people can tolerate. Shorter transport delay of insulin and hepatic glucose production delay produce better control effect, while the insulin secretion delay has almost no impact on the glucose level. Furthermore, if the injection dose is large enough, the system has a stable periodic solution under a predefined control threshold, and the control effect is better when the injection dose is larger, that is, the glucose concentration is lower and the period between two injections is longer.