The electronic, the magnetic and the orbital structures of KCrF3 are studied by first principles in its recently identified crystallographic phases (tetragonal and cubic) [Margadonna and Karotsis 2006 J. Am. Chem. Soc. 128 16436]. In tetragonal phase, both generalized gradient approximation (GGA) and GGA+U calculations show that the ground state is the A-type antiferromagnetic (A-AFM) configuration with G-type orbital ordering pattern. Our calculations show that the orbital structures and the magnetic configurations can be measured by the optical conductivity. In the cubic state, the GGA calculations show that the ground state is ferromagnetic half metal state, while the GGA+U(Ueff = 3.0 eV) calculations show that the A-AFM insulator phase is the ground state. Our calculations indicate that the electron-electron interactions rather than the electron-phonon interactions are the driving forces behind the orbital order.