The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. The present invention relates to a method and an apparatus for performing random access in a wireless communication system. More specifically, proposed is a method of, when a terminal intends to perform random access through multiple PRACH preamble transmission in an unlicensed band, determining whether to change or reset a CP length of a channel access procedure gap or a PRACH preamble according to the number of multiple PRACH preamble transmissions.