Provided is a partition and segmentation on-line positioning method for small-current grounding faults, which comprises first utilizing a pressure measuring unit (PMU) voltage measurement device arranged on a converting station busbar and a plurality of PMU current measurement devices arranged on a circuit to respectively measure zero-sequence voltage of the converting station busbar and zero-sequence currents on each measurement point on the circuit, then determining the upper and lower stream relation between each measurement point and fault points according to the phase-relation between the zero-sequence current of each measurement point on the circuit and the zero-sequence voltage of the busbar of the converting station, and further obtaining a fault interval with the measurement points serving as boundary nodes. The partition and segmentation on-line positioning method for the small-current grounding faults can fast and accurately determine the fault areas and the fault points of small-current grounding under the condition of non-outage, is not influenced by grounding fault types, does not need additional signal devices, is simple to operate, and has high reliability. The partition and segmentation on-line positioning method for the small-current grounding faults can help maintenance personnel to remove faults in time, and is suitable for various fault conditions of metallic grounding, grounding through voltaic arcs, grounding through transition resistors and the like.