The invention discloses an annular omnidirectional antenna and belongs to the technical field of broadband wireless communication systems. The antenna comprises a printed circuit board with a double-sided copper-clad structure; a front radiation layer comprises a split ring, a parasitic ring, a microstrip feeder line and a loading frame; an included angle between two ends of the split ring is 270+/-10 degrees; one end of the split ring is overlapped with the extending tail end of the microstrip feeder line and is in feed connection with the microstrip feeder line; the parasitic ring is positioned in the split ring; two openings which are in central symmetry relative to the circle center of the parasitic ring are formed in the parasitic ring; the loading frame is a fold line with three sections; a back metal ground layer comprises a rectangular sub-region and an isosceles trapezoid-shaped sub-region; the parasitic ring is located outside the range of the isosceles trapezoid-shaped sub-region and is tangent to the upper bottom of the isosceles trapezoid-shaped sub-region; and the length of the upper bottom of the isosceles trapezoid-shaped sub-region is smaller than the inner diameter of the parasitic ring. The antenna has the advantages of simple and compact structure, easiness in machining and high machining precision, and is capable of meeting the requirement for electricallysmall size and can be applied to a broadband wireless communication system.