Abstract: To address the challenge of monitoring high concentrations of dissolved gases in on-load tap-changer (OLTC) oil(e.g.,acetylene exceeding 10,000 μL/L), a wide-range high-precision monitoring device has been designed. The system employs an architecture featuring "variable degassing volume and dual quantitative tube sampling and dual detectors in series and intelligent screening," which extends the measurement range based on gas-liquid equilibrium and detector response characteristics. Experimental validation confirms that the relative deviation and RSD meet the required standards across the full concentration range (from μL/L level up to 10? μL/L). This approach resolves the limitations of conventional devices, such as insufficient measurement range and signal distortion at high concentrations, thereby fulfilling the monitoring requirements for OLTC under all operating conditions.