A model of currents around Mars is proposed, upon which the distribution of magnetic field in Martian equatorial plane is calculated. In this model, there exist currents in the Martian magnetopause, the Martian ionosphere and the current sheet in the Martian magnetotail based on the observational data from satellite and appropriate assumptions. According to the continuity of the current, these currents satisfy the relation that the total current in the Martian magnetopause is equal to the summation of the total current in the Martian ionosphere and the total current in the Martian magnetotail. Superposition of the magnetic field generated by these currents and solar wind magnetic field constitutes magnetic field in the Martian equatorial plane. Results obtained through the model of Martian currents are consistent with observational results through satellite and those gained by other methods.