A series of numerical simulations are conducted (using GFDL CM2.1) to investigate the global mean precipitation and temperature change in response to climate variation. Experiments under different carbon dioxide (CO_2) forcing indicate an obvious precipitation hysteresis. There is a significant linear relationship between global mean precipitation and surface temperature, but precipitation is also influenced directly by CO_2 concentration. During the experiments in which CO_2 concentration rises up and then falls back, precipitation change lags behind surface temperature, which leads to the precipitation hysteresis. While CO_2 increasing, the enhanced greenhouse effect will lead to immediate intension of atmospheric long-wave absorption, which will bring net radiative energy income to atmosphere. To balance the energy budget, upward latent heat has to be restrained, so the additional CO_2 has inhibiting effect on precipitation. The subsequent warming mainly induces increasing in outgoing long wave radiation at TOA and backward long wave radiation at surface, which is equivalent to a radiative cooling for atmosphere, and then causes precipitation rising. While CO_2 decreasing, on the contrary, the subdued greenhouse effect tends to intensify precipitation and the temperature reduction will reduce the precipitation. Different effects on precipitation from temperature and CO_2 determine the precipitation hysteresis.