The surface air temperature change over China and the globe in the twentieth century is simulated by an atmospheric general circulation model. The observed sea surface temperature and sea ice distributions provided by the PCMDI from year 1870 to 2006 are prescribed in the model. The results show that the model performs well in simulating the global mean of the surface temperature in the twentieth century, since the variations and the amplitudes are comparable to the observations. However, the reproducibility of the surface air temperature over China is lower than that over the globe, while it is still acceptable. The wavelet transform results show that the powers mainly concentrate within the bands of interannual, decadal, or even longer interdecadal time scales, while the most significant periods are within the band less than 10 year, and the decadal variations are also significant in the late twentieth century. Analyses of the variance for the time series show that the external forcing accounts for about 80%, which may explain why the simulation can reproduce the observations so well.