Abstract: To address the issues of high voltage stress and limited step-down ratio in traditional single-stage high step-down converters, a hybrid high step-down DC-DC converter with low voltage stress is proposed. By introducing a transformer after a pre-step-down capacitor network, enhanced step-down conversion and electrical isolation are achieved. Compared with traditional converters such as forward and half-bridge topologies, the pre-step-down capacitor network reduces reliance on turns ratio of transformer in high step-down applications. This helps to avoid associated issues such as high leakage inductance and excessive winding voltage. The proposed converter adopts a split-capacitor structure at the input, effectively reducing the start-up and steady-state voltage stress on each active switch. Moreover, the simplified control timing helps to achieve zero-voltage switching(ZVS) for multiple active switches. Finally, a prototype with 400-800 V input, 12 V/120 W output is built, and peak efficiency is 92.9% under 800 V input. Experimental results validate the theoretical analysis and confirm the feasibility of the proposed high step-down isolation conversion scheme.