Abstract: The present invention relates to a method for searching trunks in exchange systems that a subsystem searches a standby idle trunk for preparing a next trunk usage, stores information of the standby idle trunk and then processes a current call service by connecting the preset trunk when the call is required, whereby minimizing load of the system as well as improving a search speed of the trunk. The exchange system applied to the present system is composed of a subscriber call processing unit, a number decoding unit, a routing control unit, and a plurality of switching subsystems. The present invention has advantages to prevent the processor load from increasing according to the call processing as well as improve the system stability efficiently.