Abstract: A class of positive periodic functional differential equations are investigated by nonlinear functional analysis including the fixed point index theorem, operator theorem and cone theory. Compared with the earlier works as shown in reference, both the existence and multiplicity theorems of such functional differential equations with infinite delay are obtained. An example is given to illustrate the conclusion drawn, where the effectiveness of the existence and multiplicity theorems is further proved by Hematcpoiesis model for the positive periodic solutions to the functional differential equations with infinite delay.