A method for producing a polyurethane elastic fiber according to the present invention contains the steps of: [1] producing a polyurethane urea polymer (A) having a number average molecular weight ranging from 12,000 to 50,000, and represented by general formula (1); [2] preparing a spinning dope by adding the polyurethane urea polymer (A) to a polyurethane urea polymer (B); and [3] spinning a polyurethane elastic fiber using the spinning dope. In the formula, R1 and R2 are an alkyl group or a hydroxyalkyl group, R3 is an alkylene group, a polyethyleneoxy group or a polypropyleneoxy group, R4 is a diisocyanate residue, X is a urethane bond or a urea bond, R5 and R6 are a diisocyanate residue, P is a diol residue, Q is a diamine residue, UT is a urethane bond, UA is a urea bond, each of k, 1, m and n is 0 or a positive number.