Patent citation network analysis is an important patent analysis method to find out the fundamental or critical technology developments in a field. The way to construct the patent citation network is typically through an investigation of backward and forward citations. While past research mostly treat all backward citations of a patent equally, this research proposes a novel method to draft patent citation networks based on subject feature through patent classification codes. This allows us to remove patents that are of less interest and construct a more reasonable network. Moreover, the topology of our patent citation network is not prone to the weights set by the researcher.