  We study the thermodynamics of QCD system under external magnetic field via
the 2+1 flavor Polyakov-loop quark-meson model. To incorporate quantum and
thermal fluctuations, the functional renormalization group approach is
implemented in our work. Pressure, entropy density, magnetic susceptibility and
other thermodynamic quantities are calculated and analyzed to investigate the
effect of magnetic field on the QCD system. The calculated results are in
reasonable agreement with lattice QCD simulations and perturbation theory. We
then give an intuitive picture for the response of QCD system to the magnetic
field.
