The invention relates to the technical field of tap water supply pipe network leakage measurement, in particular to a DMA zone pipe network leakage online detecting and positioning system and a detecting and positioning method thereof. The system comprises a DMA zone tap water main pipeline, a first DMA zone tap water branch pipeline, a second DMA zone tap water branch pipeline,..., an N-1 DMA zone tap water branch pipeline, an N DMA zone tap water branch pipeline, a data collecting unit, pressure detecting units, sound wave detecting units, a system server and a work station. The data collecting unit is installed on the tap water main pipeline in the position of an inlet of a DMA zone, and data are uploaded to the system server through a GPRS/3G/4G module. The pressure detecting units or the sound wave detecting units, or the pressure detecting units and the sound wave detecting units are installed on the first DMA zone tap water branch pipeline, the second DMA zone tap water branch pipeline,..., the N-1 DMA zone tap water branch pipeline and the N DMA zone tap water branch pipeline correspondingly, and the pressure detecting units and the sound wave detecting units upload data to the system server through the GPRS/3G/4G module. The system server communicates with the work station through the industrial Ethernet. The DMA zone pipe network leakage online detecting and positioning system and the detecting and positioning method thereof are suitable for underground water supply pipe networks, installation is easy, and leakage detecting and positioning of terminal pipeline networks of all the urban DMA zones are well achieved.