The present disclosure provides an apparatus for setting a gain of a RF repeater includes: a synchronization signal power calculator configured to determine an average received power level of a synchronization signal received over a predetermined number of times as a synchronization signal power; a downlink power calculator configured to calculate a downlink input power according to a power ratio of synchronization signal to data channel signal based on the synchronization signal power; and a downlink gain setting unit configured to calculate a downlink gain by subtracting the downlink input power from a downlink output power determined by hardware specifications to set the downlink gain.