A method for relative quantitative analysis of a polymer by MALDI mass spectrometry, comprising the steps of: (S1) preparing a plurality of polymer specimens having a thickness variation of 30% or less by electrospray of a solution containing a polymer sample and a matrix through a mask for each concentration of the polymer sample; (S2) obtaining a MALDI mass spectrum by irradiating a laser to each of the plurality of polymer specimens; and (S3) preparing a quantitative calibration curve with a signal of a polymer sample from peak results of the MALDI mass spectrum, wherein the preparing the polymer specimen by electrospray through the mask comprises the steps of: (i) preparing an electrospray apparatus comprising a sample plate and an electrospray main nozzle and mounting the mask on the sample plate; and (ii) electrospraying the solution containing the polymer sample and the matrix onto the mask-mounted sample plate by the main nozzle , wherein the mask comprises a hole through which the polymer sample solution electrosprayed from the main nozzle passes onto the sample plate so as to obtain a polymer specimen having a small thickness variation on the sample plate, characterized in that the electrospray apparatus further comprises an auxiliary nozzle surrounding the main nozzle and coaxial with the main nozzle , and the electrospraying the polymer sample solution onto the sample plate by the main nozzle further comprises the step of spraying a solvent by the auxiliary nozzle to prevent the matrix from being deposited around the main nozzle . (S1) preparing a plurality of polymer specimens having a thickness variation of 30% or less by electrospray of a solution containing a polymer sample and a matrix through a mask for each concentration of the polymer sample; (S2) obtaining a MALDI mass spectrum by irradiating a laser to each of the plurality of polymer specimens; and (S3) preparing a quantitative calibration curve with a signal of a polymer sample from peak results of the MALDI mass spectrum, wherein the preparing the polymer specimen by electrospray through the mask comprises the steps of: (i) preparing an electrospray apparatus comprising a sample plate and an electrospray main nozzle and mounting the mask on the sample plate; and (ii) electrospraying the solution containing the polymer sample and the matrix onto the mask-mounted sample plate by the main nozzle , (i) preparing an electrospray apparatus comprising a sample plate and an electrospray main nozzle and mounting the mask on the sample plate; and (ii) electrospraying the solution containing the polymer sample and the matrix onto the mask-mounted sample plate by the main nozzle , wherein the mask comprises a hole through which the polymer sample solution electrosprayed from the main nozzle passes onto the sample plate so as to obtain a polymer specimen having a small thickness variation on the sample plate, characterized in that the electrospray apparatus further comprises an auxiliary nozzle surrounding the main nozzle and coaxial with the main nozzle , and the electrospraying the polymer sample solution onto the sample plate by the main nozzle further comprises the step of spraying a solvent by the auxiliary nozzle to prevent the matrix from being deposited around the main nozzle . <EOS>