The effect of the Martian crustal magnetic field on ion escape is the focus of considerable interest. Directions of magnetic fields near Mars determined by the interaction between Mars’ crustal and interplanetary magnetic fields have been suggested to play a significant role on ion transport around Mars. In this study we investigate the physical mechanism of deflection of O 2 + ion flow in two typical magnetic field orientations at the horizontal plane in the Martian ionosphere by performing 3D multifluid Hall magnetohydrodynamic simulations. Cross validation of the simulation results from two cases with the G110 crustal field model and equivalent source dipole model reveals that due to the Hall electric force, O 2 + ion flow tends to be accelerated eastwards in the region occupied by outward magnetic fields, and westwards in the region with inward magnetic fields. These results are helpful for understanding the impact of magnetic fields on the deflection of ionospheric ions in the Martian space environment.