  In this paper we investigate the electronic and magnetic properties of
K$_{x}$Fe$_{2-y}$Se$_{2}$ materials at different band fillings utilizing the
multi-orbital Kotliar-Ruckenstein's slave-boson mean field approach. We find
that at three-quarter filling, corresponding to KFe$_{2}$Se$_{2}$, the ground
state is a paramagnetic bad metal. Through band renormalization analysis and
comparison with the angle-resolved photoemission spectra data, we identify that
KFe$_{2}$Se$_{2}$ is also an intermediate correlated system, similar to
iron-pnictide systems. At two-third filling, corresponding to the
Fe$^{2+}$-based systems, the ground state is a striped antiferromagnetic (SAFM)
metal with spin density wave gap partially opened near the Fermi level. In
comparison, at half filling case, corresponding to the Fe$^{3+}$-based
compounds, besides SAFM, a $N\acute{e}el$ antiferromagnetic metallic ground
state without orbital ordering is observed in the intermediate correlation
range, and an orbital selective Mott phase (OSMP) accompanied with an
intermediate-spin to high-spin transition is also found. These results
demonstrate that the band filling and correlation control the electronic state,
Fermi surface topology and magnetism in K$_{x}$Fe$_{2-y}$Se$_{2}$.
