  We prove the global well-posedness for the 3-D micropolar fluid system in the
critical Besov spaces by making a suitable transformation to the solutions and
using the Fourier localization method, especially combined with a new $L^p$
estimate for the Green matrix to the linear system of the transformed equation.
This result allows to construct global solutions for a class of highly
oscillating initial data of Cannone's type. Meanwhile, we analyze the long
behavior of the solutions and get some decay estimates.
