Embodiments of the present invention disclose a method for transmitting baseband signals. The method includes: when downlink traffic volume in an area among areas covered by multiple remote radio frequency units RRUs is lower than a preset threshold, generating or receiving a group of downlink baseband signals, where the group of downlink baseband signals correspond to all RRUs in the area; and transmitting the group of downlink baseband signals to each RRU in the area, so that each RRU generates downlink radio frequency signals based on the downlink baseband signals and sends the downlink radio frequency signals. Accordingly, the embodiments of the present invention further disclose a method for transmitting baseband signals and a BBU. With the technical solutions, the bandwidth for transmitting baseband signals is greatly lowered, implementation is easy, and complexity of a system is reduced.