The invention discloses a capacitor-loaded stepped impedance type tri-polarization half-slot antenna, and relates to a slot antenna. The antenna comprises three perpendicularly-placed single-polarized antennas (13), wherein each antenna (13) comprises a dielectric substrate (1), and a metal ground (2) and a radiation slot slit (3) on the dielectric substrate (1), and a microstrip feeder line (4); the radiation slot slit (3) is formed in the metal ground (2); one end of the radiation slot slit (3) is in short circuit while the other end (6) of the radiation slot slit is in open circuit; a low resistance slot slit (8), which is formed by multiple parallel capacitors (7) that are bridged on the edge of the radiation slot slit (3), is formed in the part, close to the open circuit end, of the radiation slot slit (3); a high resistance slot slit (9) is formed in the rest part of the radiation slot slit (3); and an antenna port (10) is formed in one end of the microstrip feeder line (4) while the other end of the microstrip feeder line (4) is in open circuit, and crosses over the high resistance slot slit (9) and extends for a certain length. The antenna is in multi-band operation, so that the antenna dimensions, and the conditions of crossed polarization and shielding can be reduced, and isolation among ports can be improved.