Disclosed is a method for producing a nanometer zinc oxide from low-grade zinc oxide ore by ammonia decarburization. The method comprises: taking ammonia water-ammonium bicarbonate solution as a leaching agent; adding 0.3-0.5 kg sodium fluorosilicate to per cubic meter of the leaching agent; leaching low-grade zinc oxide ore with the leaching agent; and adding 50-60 kg slaked lime to per cubic meter of leached solution to carry out decarburization treatment. The obtained nanometer zinc oxide powder has purity of 99.7% or up, uniform particle size distribution (average particle size of 10-28 nm), specific surface area of 107 m2/g or up, good fluidity and good dispersity. The treatment method of the present invention is low in energy consumption and high in efficiency, and the leaching agent can be recycled. The final leached residue subject to the leaching treatment, without destruction of original mineral component phase composition, can still be used for brick making, so as to achieve dual purposes of economy and environment protection, and has a high economic value and social value.