Abstract: Cassiterite is an important ore mineral in tin polymetallic deposits. Using cassiterite for dating tin polymetallic deposits has become one of the most direct method to obtain the mineralization age of the deposits. However, due to the low uranium content and high common lead characteristics of cassiterite, the main problems and technical difficulties in situ U-Pb dating method for cassiterite lie in the development of ideal standards and the accurate of common lead correction. This paper constrains the mineralization age of the Laozhailing Cu-Sn deposit in Yongzhou City, Hunan Province, by optimizing the technology. The Laozhailing Cu-Sn deposit is a vein-type tin polymetallic deposit, which is mainly composed of tin quartz veins, cataclastic greisenized granite, and greisen. Three samples, including 16LZ01, 16LZ02, and 16LZ03, were obtained with Tera-Wasserburg U-Pb lower intersection ages of 222.0±1.5Ma (MSWD=1.6, n=37), 220.5±3.7Ma (MSWD=2.9, n=28), and 225.0±1.6Ma (MSWD=1.3, n=31), respectively. These results indicated mineralization in the Late Indosinian period. The mineralization of the Laozhailing Cu-Sn deposit is closely related to the magmatic hydrothermal activity of the Yangmingshan complex granites. The results of this study provide important chronological evidence for the magmatic hydrothermal origin of the Laozhailing Cu-Sn deposit.