The invention provides a slot array loading four-unit multi-frequency high-isolation microstrip MIMO antenna and relates to the field of research of antennas in passive devices. The four-unit antenna unit is provided with a T-shaped feed coupling line port, and a slot array is periodically loaded on a radiation patch to realize polarization diversity, so that the antenna isolation is improved, the four-unit MIMO antenna system inhibits coupling among antennas, excites more resonance frequency points and improves a high-order mode directional diagram, and the size of the antenna is greatly reduced; the coupling feeder line and the radiation unit adopt microstrip lines, so that the section of the antenna is low and the antenna is easy to process; and the designed antenna has multi-frequency point frequency working characteristic and stable polarization diversity characteristic, and a dielectric substrate is low in price and easy to buy, in a word, the slot array loading four-unit multi-frequency high-isolation microstrip MIMO antenna is low in manufacturing cost and easy to process, realizes batch production and has a great actual application value.