A distributed antenna system (DAS) for multi-carrier and multi-frequency band based on an O-RAN standard in an open radio access network (O-RAN)-based mobile communication network is provided. The DAS includes an O-RAN remote unit (RU) connected to a fronthaul network according to an O-RAN split option specification of base station transceiver systems (BTSs), and comprising a plurality of O-RAN RUs to accommodate a plurality of carriers and a plurality of frequency bands, and a channel combiner to which outputs of the plurality of O-RAN RUs are combined. The channel combiner is an analog combiner. The DAS further includes an optical distribution unit (ODU) connected to the analog combiner, and a radio unit (RU) connected to the ODU. The RU includes an optical receiving unit (ORU), a high power amplifier (HPA), a low noise amplifier (LNA), and a duplexer or filter.