The present invention relates to a system and method for controlling a network access of a network packet on the basis of a thread which is inserted into a process through code injection. The network access control system according to the present invention comprises: a process inspecting unit for detecting a code injection-based thread included in a process; and a network monitoring unit for performing network filtering so as to detect a network packet having access to a network, and, if a communication subject of the detected network packet is the code injection-based thread, blocking the traffic of the detected network packet.