A distributed antenna system, comprising: a source unit; at least two digital-analog expansion units, one of the at least two digital-analog expansion units is connected to the source unit through an optical fiber, and two adjacent ones of the at least two digital-analog expansion units are cascaded through an optical fiber; and at least two remote cascade chains, each remote cascade chain including a plurality of remote units cascadingly connected by means of radio frequency cable, and a first remote unit of the remote cascade chain being connected to one of the at least two digital-analog expansion units by means of radio frequency cable; wherein the digital-analog expansion unit is configured to perform, through a first baseband processing module inside the digital-analog expansion unit, a baseband processing operation on a downlink digital radio frequency signal transmitted by the source unit through an optical fiber, and perform digital-to-analog conversion through a first signal conversion module inside the digital-analog expansion unit, to obtain a downlink analog radio frequency signal to be transmitted to the remote cascade chain; or the digital-analog expansion unit is configured to perform, through the first signal conversion module, analog-to-digital conversion on an uplink analog radio frequency signal transmitted by the remote cascade chain, and perform a baseband processing operation through the first baseband processing module, to obtain an uplink digital radio frequency signal to be transmitted to the source unit through an optical fiber; wherein the remote unit is configured to perform analog radio frequency signal interaction with a terminal device, and two adjacent ones of the remote units performing analog radio frequency signal interaction by means of the radio frequency cable; wherein one of the at least two digital-analog expansion units is correspondingly connected to at least one of the at least two remote cascade chains, and each of the at least two digital-analog expansion units includes a radio frequency front end module connected to the first remote unit of the corresponding one of the at least two remote cascade chains. a source unit; at least two digital-analog expansion units, one of the at least two digital-analog expansion units is connected to the source unit through an optical fiber, and two adjacent ones of the at least two digital-analog expansion units are cascaded through an optical fiber; and at least two remote cascade chains, each remote cascade chain including a plurality of remote units cascadingly connected by means of radio frequency cable, and a first remote unit of the remote cascade chain being connected to one of the at least two digital-analog expansion units by means of radio frequency cable; wherein the digital-analog expansion unit is configured to perform, through a first baseband processing module inside the digital-analog expansion unit, a baseband processing operation on a downlink digital radio frequency signal transmitted by the source unit through an optical fiber, and perform digital-to-analog conversion through a first signal conversion module inside the digital-analog expansion unit, to obtain a downlink analog radio frequency signal to be transmitted to the remote cascade chain; or the digital-analog expansion unit is configured to perform, through the first signal conversion module, analog-to-digital conversion on an uplink analog radio frequency signal transmitted by the remote cascade chain, and perform a baseband processing operation through the first baseband processing module, to obtain an uplink digital radio frequency signal to be transmitted to the source unit through an optical fiber; wherein the remote unit is configured to perform analog radio frequency signal interaction with a terminal device, and two adjacent ones of the remote units performing analog radio frequency signal interaction by means of the radio frequency cable; wherein one of the at least two digital-analog expansion units is correspondingly connected to at least one of the at least two remote cascade chains, and each of the at least two digital-analog expansion units includes a radio frequency front end module connected to the first remote unit of the corresponding one of the at least two remote cascade chains.