Western Zhou Dynasty (ca. 1046–771 BC) was established soon after conquering the Shang Dynasty (ca. 1600–1046 BC) and brought about the earliest enfeoffment system in Chinese history. Yan was one of the vassal states of the same clan as Zhou. According to historical records, the capital of Yan state was located near Yan mountain, which is now known as the Liulihe site in the Fangshan District, Beijing. This study carries out the high-precision dating of two newly discovered Western Zhou Dynasty noble tombs at the Liulihe site. The man in tomb M1902 participated in the groundbreaking ceremony of Yan’s capital according to inscriptions on the bronze vessel found in this tomb. Samples of different materials, especially different parts of human skeletons from the tombs, were selected to form a sample series in chronological order. Wiggle-matching models were established in OxCal program based on the growth and development time of different teeth and bones of human skeletons. More accurate ages were acquired for the death of the individuals. The results indicate that the most probable distribution range of the death date of the individual in M1902 is about 1045–1010 BC. The radiocarbon dates of M1902 give important chronological information about the founding of Yan state, and they are very close to those of the year in which King Wu of Zhou conquered the Shang Dynasty.