A Brillouin optical correlation domain analysis (BOCDA) system using time-domain data processing for concurrently interrogating a plurality of sensing positions is proposed, where the time-domain data processing combined with differential measurement effectively enhances the measurement range and measurement time as much as the spatial resolution of the BOCDA system. In the experiment, the distribution of the Brillouin gain spectra (BGS) along a 10.15 km test fiber is successfully obtained with a spatial resolution less than 5 cm by concurrently interrogating 980 correlation peaks.