We have studied the spatial structure of the three dimensional large-scale pattern of the Galactic Magnetic Field using the polarization maps obtained by the WMAP satellite at 22 GHz. By using different models of the large-scale magnetic field of the Milky Way and a certain model for the cosmic rays electron distribution, we predict the expected polarized synchrotron emission. Using a Maximum Likelihood method, we explore the parameter values which best reproduce the WMAP data and obtain the marginal probability distribution for each of them. The model that better reproduces the observed map of polarization is an axisymmetric model with radial dependence of the strength of the magnetic field.