To address the challenges of low sensitivity and high misjudgment rates in detecting single-phase open-circuit faults in distribution networks, due to their diverse fault forms and lack of distinct current characteristics, a section location method based on the magnitude difference of negative-sequence voltage is proposed. First, a unified analytical model for various types of single-phase open-circuit faults is established, and the relationships between phase voltages and negative-sequence voltages on the source side and load side at the breakage point are derived. The results show that under various complex fault scenarios, including open-circuit without grounding, single-side grounding, and double-side grounding (Rd＞5 Ω), the negative-sequence voltage on the source side is close to zero, while that on the load side exceeds 0.3 times of the normal voltage. Moreover, a significant difference in negative-sequence voltage magnitude exists only across the faulted section, whereas adjacent non-faulted sections exhibit nearly identical values. Based on this characteristic, the method further utilizes low-voltage side measurements from intelligent terminals of distribution transformers to estimate the medium-voltage line negative-sequence voltage. A fault section location scheme is then constructed using the magnitude differences of negative-sequence voltages between adjacent sections. Simulation results verify that the proposed method achieves reliable fault section localization under various compound single-phase open-circuit grounding fault conditions.