In this paper, tree-ring width chronologies of Platycladus orientalis were developed from the southern Taihang Mountains in Hebei Province. The response of tree radial growth to hydrothermal change was analyzed, and the mean relative humidity from May to July during the past 167 years was reconstructed. The results showed that tree radial growth of Platycladus orientalis responded significantly and positively to June precipitation, and negatively to mean temperature and the maximum in May, June, and July. The tree radial growth of Platycladus orientalis was restricted by hydrothermal conditions in late spring and early summer. The reconstruction showed that there was a markable change in humidity and dryness during the recent 167 years. Obvious dry periods occurred in 1876-1877, 1900-1901, 1904-1912, 1918-1921, 1926-1930, and 1933-1935, and humid period occurred in 1871-1873, 1882-1884, 1888-1890, 1893-1895, 1953-1956, 1971-1972, and 2002-2003. The reconstruction series was negatively related to the drought and flood level index at the 0.01 significance level. Cycle analysis showed that the reconstruction of relative humidity from May to July during the past 167 years had periods of approximately 2-4 years, 7.71 years, and 60 years.