The sciences of astronomy, geography and mathematics of the Han dynasty took the lead in the world of that time. The astronomy was very advanced in the Han dynasty due to the need for agricultural production. There were three main cosmic theories, i.e., the “gaitian”, the “huntian” and the “xuanye” theories; there were also abundant accurate astronomic records, such as the Tianguan Shu of the Shiji, the Tianwen Zhi of the Hanshu and of the Hou-Hanshu; and the imperial government announced several well-compiled accurate calendars, such as the Taichu Li and the Sifeng Li. Likewise, the geography was also very advanced in the Han dynasty, which had some theoretic works, e.g. the “Dili” (or Geography) in Huainanzi, and preserved abundant geographic records, such as the Hequ Shu of the Shiji and the Dili Zhi of the Hanshu, etc., as well as countless rather accurate maps. Mathematics was also very prominent in the Han dynasty due to the need for measurement in astronomy and geography. There were many mathematical works, the best known of them was the Jiuzhang Suanshu.