A system and method for performing a traffic process in an integrated network of a VoIP (Voice over Internet Protocol) network and a PSTN (Public Switched Telephone Network) are provided. The system includes: a softswitch which has a plurality of ASPs (Application Server Processes), transmits a data signal to other nodes through an ASP that is selected from among the ASPs, and transmits a heartbeat request message when a CPU (Central Processing Unit) utilization ratio and an SCTP (System Control Transmission Protocol) level congestion of the ASPs exceed respective reference points according to AS (Application Server)/ASP information; and a signaling gateway which updates the reference points of the CPU utilization ratio and the SCTP level congestion in response to the heartbeat request message and transmits a heartbeat acknowledgement message to the softswitch, and checks the CPU utilization ratio and the SCTP level congestion for a plurality of active ASPs within a predetermined CIC (Circuit Identification Code) or SSN (Sub-System Number) range according to the AS/ASP information, to determine the selected ASP when the signaling gateway receives data signal from outside and traffic is distributed.