© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0). We continuously observed the Sun's shadow in 3 TeV cosmic-ray intensity with the Tibet-III air shower array since 2000. We find a clear solar-cycle variation of the deficit intensity in the Sun's shadow during the periods between 2000 and 2009. The MC simulation of the Sun's shadow based on the coronal magnetic field model does not well reproduce the observed deficit intensity around the solar maximum. However, when we exclude the transit periods during ICMEs towards to the Earth, the MC simulation shows better reproducibility. In the present paper, we report on the MC simulation and the analysis method of the Sun's shadow observed by the Tibet-III array.