This paper describes the general moisture conditions and the annual and seasonal trends of temperature, precipitation, potential evapotranspiration and aridity/humidity index from 1971 to 2000 in China. Observed climatic data from 616 meteorological stations over China's land surface were used. Potential evapotranspiration was calculated by the Penman-Monteith model with a modified net radiation part to accommodate China's unique climatic conditions. According to the aridity/humidity index, a ratio of potential evapotranspiration to precipitation, four moisture regional types were delineated gradually from the southeast to the northwest, i.e. humid, subhumid, semiarid and arid throughout China. Linear regression was performed on the 30-year time series of the four climate factors in order to detect possible trends. The results confirm the obvious spatial and temporal difference of climate trends. Surface air temperature has increasing trends almost all over China especially in winter. Most stations are statistically significant. Annual precipitation shows increasing trends at more than half of the stations, and the increasing trends mainly occur in summer and winter while the decreasing trends occur in spring and autumn. However, most stations are not statistically significant. Potential evapotranspiration has decreasing trends in most stations and nearly half of the stations are statistically significant. Annual aridity/humidity index shows primarily decreasing trends with a distribution nearly the same as the increasing trends of precipitation. The index has the decreasing trends in spring and summer and the increasing trends in autumn and winter. The results suggest that it is necessary to consider precipitation and potential evapotranspiration simultaneously to describe the moisture conditions exactly.