The invention discloses an ion thruster discharge chamber magnetic pole structure which comprises a lower magnetic pole (1), a middle magnetic pole (2), an upper magnetic pole (3), a lower pole shoe (4), a middle pole shoe (5) and an upper pole shoe (6). The lower pole shoe (4), the middle pole shoe (5) and the upper pole shoe (6) are correspondingly connected with the lower magnetic pole (1), the middle magnetic pole (2) and the upper magnetic pole (3). The structure further comprises permanent magnets (9 and 10). A magnetic force line loop is formed among the magnetic poles through the pole shoes (4, 5 and 6) and the permanent magnets (9 and 10). A loop tip cusped magnetic field is formed in a discharge chamber. The structure is characterized in that positive pole cylinders (7 and 8) of the discharge chamber are arranged in the cusped magnetic field, all the magnetic poles extend to the inner surfaces of the positive pole cylinders (7 and 8) and are charged with negative electricity relative to the positive pole cylinders (7 and 8), and a discharge chamber negative pole (11) installed on the lower pole shoe (4) directly extends into the discharge chamber under the circumstance without the positive pole cylinders ahead. The invention further discloses a design method for the ion thruster discharge chamber magnetic pole structure. When the structure is used, the primary electron utilization rate can be increased, and the discharging efficiency and the beam uniformity are improved.