Disclosed are an antenna adaption method and device in a wireless communication system, the method comprising the steps in which: a terminal confirms that an operation is performed in a second antenna mode; whether a synchronization signal/physical broadcast channel block (SSB) to be measured exists in an activated bandwidth part is determined; and if the SSB to be measured does not exist in the activated bandwidth part, an SSB is measured in a first measurement gap set by a base station, wherein the second antenna mode is a mode operating by being set to the number of maximum multi-input multi-output (MIMO) layers, which is less than the number of maximum MIMO layers notified by the terminal to the base station through capacity reporting.