Currently, the coal-fired power plants annually emit approximately 16−18 million tons of fly ash and bottom ash in Vietnam. By the end of 2021, the accumulated ash-slag in waste dumps will reach about 50 million tons. A promising solution to this environmental challenge lies in the partial replacement of clay with fly ash in cement clinker production, however, industrial-scale implementation has faced some technological difficulties. This paper presents the results of the pilot research project “Research on perfecting the technology of using fly ash to substitute clay in clinker cement manufacturing” which has successfully addressed these challenges. A key innovation of the project has been the development of a standardized curve for fly ash analysis and raw material mixing. This curve enables precise control of the fly ash content in the clinker production process, ensuring consistent quality and reducing the risk of defects. Furthermore, the project has conducted pilot studies using raw materials of Vicem Hoang Thach Cement Company, Vietnam. These studies have achieved valuable insights into the optimal fly ash-to-clay substitution ratio and the necessary adjustments to the production process. To facilitate industrial-scale implementation, the project has also designed and manufactured specialized equipment for the production line. Through these efforts, the project has successfully produced over 99,000 tons of clinker cement using fly ash as a partial clay substitute. The project has also developed comprehensive guidelines for other cement factories in Vietnam to adopt this sustainable practice. The results of this research represent a significant step forward in reducing waste from thermal power plants and promoting a more circular economy in the cement industry.