A peak-width quantitation method for flow-injection microwave plasma torch atomic emission spectrometry was proposed. Sensitivity and linearity of the peak-width quantitation were investigated under different emission intensities. Recoveries of Zn2+, Cu2+ and Ag+ existing in various matrix were determined by using the peak-width quantitation, and were compared with the results obtained by the peak-height method. The results indicated that the peak-width quantitation can efficiently remove matrix interference in the FI-MPT-AES system, and expand its linear determination range. The peak-width quantitation (recovery: 92%-107%) surpasses conventional peak-height method (recovery: 61.3%-122%). Optimized determination conditions were as follows: the sampling volume was 350 mL, the flow rate of the carrier was 1.5 mL·min-1, the power of microwave was 110 W, the flow rates of the carrier gas and working gas (argon) were 1.4 and 0.4 L·min-1, respectively.