A method and apparatus for controlling a Transmit power (TX power) of an indoor Base Station (BS) in a broadband wireless communication system. An operation of the indoor BS includes receiving received channel quality information on the indoor BS from at least one Mobile Station (MS), increasing in steps the TX power by as much as a basic unit amount and, determining whether an MS located outside a building has accessed the indoor BS using the received channel quality information in every increase and, when the MS located outside the building has accessed the indoor BS, decreasing the TX power of the indoor BS.