With semi-classical approximation, thermodynamic properties of Fermi gas trapped in both gravity field and magnetic field are studied. By using theoretical analysis and numerical simulation, influence of gravity field on thermodynamic properties of the system in strong magnetic field is analyzed. It shows that, compared with the case of strong magnetic field only, gravity field makes the energy, chemical potential reduced. With rising temperature, influence of gravity field on chemical potential is gradually enlarged. There is a maximal influence of gravity field on heat capacity. Gravity field makes oscillation of heat capacity almost unchangeable while oscillation center of chemical potential shift down.