The present invention is directed to a reactive dye-dyeable polyurethane-urea elastic yarn including a reaction product of at least two polyols, a diisocyanate compound, a diamine chain extender, an amine chain terminator, and a diethylenetriamine compound, wherein one of the polyols is polyethylene glycol, which is included in an amount of 20 to 30.0 mol % based on the total amount of the polyols, a polyurethane-urea polymer includes 10 meq/kg to 45 meq/kg of primary amine ends, and the capping ratio (CR) of the diisocyanate to the polyols is 1.8 to 2.0.