By scanning near infrared spectrum (NIRS) of wastewater with different NH3N contents,a quantitative analysis model of NH3N in wastewater was proposed.Taking into consideration the computational burden of full spectral data,successive projection algorithm (SPA) was employed to choose the feature spectral data.The selected feature variables were then used for modeling based on least squares support vector machine (LSSVM).The proposed model resulted in RMSEP=3.210 8,correlation coefficient=0.984 4,and RPD=5.681 2.Compared to the fullspectral LSSVM model and partial least squares (PLS) model,the proposed SPA and LSSVM model compressed 512dimentional fullspectral data into 28dimentional ones whose computation burden is 5.47% of the fullspectral data.Nevertheless,the precision of the proposed model is similar to the fullspectral LSSVM model and is better than the fullspectral PLS model.The proposed method has good guidance significances for rapid measurement of NH3N and lowdimensional variable modeling.