A waveguide slotted array antenna comprises a feed layer and a radiation layer, wherein the feed layer is located below the radiation layer, and the radiation layer comprises a first radiation unit, a second radiation unit, a third radiation unit and a fourth radiation unit which are stacked from bottom to top; the first radiation unit comprises a first flat metal plate and a first radiation array arranged on the first flat metal plate, the second radiation unit comprises a second flat metal plate and a second radiation array arranged on the second flat metal plate, the third radiation unit comprises a third flat metal plate and a third radiation array arranged on the third flat metal plate, and the fourth radiation unit comprises a fourth flat metal plate and a fourth radiation array arranged on the fourth flat metal plate. The waveguide slotted array antenna has the advantages of low sidelobes and low cost while ensuring broad bands and high gains, and can be made small.