Rural power grids are characterized by seasonal demand fluctuations, large peak-to-valley load differences, and low average load rates. During special periods such as the Spring Festival or busy farming seasons, sudden load surges often occur, leading to severe overloading issues in transformers. Traditional mineral insulating oil can no longer adequately meet the safety requirements of high-overload distribution transformers. To address the aforementioned issues, this study leverages a newly developed multi-component mixed oil, which exhibits excellent fire resistance, thermal stability, and anti-aging properties. A 10 kV high-overload transformer incorporating this multi-component mixed oil was developed. Through routine tests, type tests, special tests, and commissioned tests, the oil parameters, fundamental performance, and overload capacity of the transformer were obtained and analyzed. The results demonstrate that the developed transformer fully complies with the current standards for mineral oil transformers and high-overload transformers. It exhibits exceptional operational safety and high overload capacity, significantly enhancing power supply reliability in regions prone to high overload conditions.