  Two dimensional statistical integrable models, such as the Ising model, the
chiral Potts model and the Belavin model, becomes integrable. Because of the
SU(2) symmetry of these models, these models become integrable. The integral
models are often parameterized by the elliptic function or the elliptic theta
function. In this paper, we study the Ising model, and we show that the
Yang-Baxter equation of the Ising model can be written as the integrability
condition of SU(2), and we gives the natural explanation why the Ising model
can be parameterized by the elliptic function by connecting the spherical
trigonometry relation and the elliptic function. Addition formula of the
elliptic function is the secret of the exact solvability of the Ising model.
