Application specific on-chip network is a promising direction for Networks on Chips (NoCs) to solve the interconnection challenges that Systems on Chips (SoCs) will encounter in the billion-transistor age. This paper presents a novel design methodology named On-Chip Network Evolution, which helps developing an on-chip network rapidly according to a specific application. To explore the network design space more efficiently, a new description language-NetC is introduced, which is a group of syntaxes that can be translated into SystemC programs.