Early masonry check dams are prone to cracking, seepage, and even collapse due to insufficient geotechnical investigation and difficulties in controlling construction quality. This paper presents a case study of the reinforcement and rehabilitation project at the Liuzhuyan Headworks on the Lianshui River in Nanzheng District. Through comprehensive on-site implementation, a suite of integrated technical measures—including foundation strengthening, structural reinforcement, scour protection, and seepage control—was applied. Following the retrofitting, the dam has operated safely and stably, with its water-retaining and flood-discharge functions fully assured; no further seepage or structural damage has occurred, demonstrating effective quality control throughout construction. The project successfully validates the technical feasibility and economic rationality of the proposed reinforcement scheme. Moreover, the quality control methodologies developed and implemented offer replicable and scalable practical experience for the rehabilitation of similar masonry check dams.