Hyperbranched polymers generated from the copolymerization of AB(2)-type monomers slowly added into trifunctional C-3 cores under various feed rates were investigated by a kinetic model. The dependences of average molecular weight, polydispersity, degree of branching (DB), and number of structural units of the hyperbranched polymers on the feed rate were calculated by a generating function method. It was found that the final PDI can be attained below 1.5 by a slow addition with the parameter of feed rate, phi, less than 1. While the AB(2) monomers fed quickly, the system with a lower content of the C-3 cores results in a broader molecular weight distribution. A high DB, about 0.66, can be achieved by addition of a small amount of C-3 cores at phi lower than 10.