An apparatus and method for preventing performance degradation of a call service in a portable terminal are provided. In the apparatus, a memory stores a Preferred Roaming List (PRL) including information about a plurality of systems and an avoidance list including information about a system to which access has failed the predetermined number or more times, and when an access attempt to originate or terminate a call to or from a specific system acquired in a weak electrical field has failed a predetermined number or more times, a controller controls reacquisition of the specific system and attempting of call origination to or call termination from the reacquired specific system.