1. A method for producing a high-purity nanometer zinc oxide from electrolytic zinc acid leaching residues by ammonia decarburization comprising: the electrolytic zinc acid leaching residue being processed by leaching, purification for impurity removal, crystallization by ammonia evaporation, drying and calcinations, comprising: ammonia water-ammonium bicarbonate solution being used as the leaching agent; wherein said ammonia water-ammonium bicarbonate solution including molar concentration c(NH 3 )=5-6 mol/L, molar concentration c(CO 3 2− )=0.85-1.0 mol/L, and 0.3-0.5 kg sodium fluorosilicate being added to per cubic meter of said leaching agent; performing heating to reduce ammonia and decarburize including adding 30-60 kg slaked lime to per cubic meter of leached solution and stirring, heating to 90-98° C. until c(CO 3 2− )≦0.3 mol/L, and then performing solid-liquid separation; refining treatment being performed including adding surfactant to the liquid after purification, wherein the adding amount equals to 20-50 g per cubic meter of said liquid after purification.