The invention discloses a ferro-tungsten composite oxide. The ferro-tungsten composite oxide comprises three elements including ferrum (Fe), tungsten (W) and oxygen, wherein Fe and W are highly dispersed in the composite oxide with molar ratio of (5.8-12.9):1, preferentially, with molar ratio of 6.8:1. The ferro-tungsten composite oxide has a total or partial three-dimensional flower petal structure, and the flower petal structure is composed of multiple petals. The invention also discloses preparation and application of the ferro-tungsten composite oxide. The preparation method is simple and practicable, the adopted precursor is commonly used metal salt such as sulfate, tungstate, is low in cost, is easy to obtain, and can reach industrial production conveniently. The obtained ferro-tungsten composite oxide with the flower petal structure as the denitrification catalyst has high catalytic activity and N2 selectivity, is wide in temperature range, and high in sulfur dioxide and water poisoning resistance, and is used for purifying or eliminating nitric oxide in flue gas from a regular source, diesel exhaust and tail gas from a lean-burning gasoline engine.