Abstract: Employing a fixed point theorem in cones, we discussed mainly the existence of positive solution to periodic problems for the first imp ulsive functional differential equations, obtained the existence positive periodic solutions of the problem for first impulsive functional differential equatio ns with delay. And we also discussed impulsive differential equations applied to biological system, for example, the Hematopoiesis model, the more general model of blood cell production, and the more general Nicholson’s blowflies model and so on.

Key words: functional differential equation, positive periodic solution, impulse, fixed point theorem