Investigations were initiated to develop terahertz (THz) techniques associated with machine learning methods of generalized neural network (GRNN) and back propagation neural network (BPNN) to rapid measure benzoic acid (BA) content in wheat flour. The absorption coefficient exhibited a maximum absorption peak at 1.94THz, which generally increased with the content of BA additive. THz spectra were transformed into orthogonal principal component analysis (PCA) scores as the input vectors of GRNN and BPNN models. The best GRNN model was achieved with 3 PCA scores and spread value of 0.2. Compared with BPNN model, GRNN model to powder samples could be considered very successful for quality control of wheat flour with a correlation coefficient of prediction (rp) of 0.85 and root mean square error of prediction (RMSEP) of 0.10%. The results suggest that THz technique association with GRNN has significant potential to quantitatively analyze BA additive in wheat flour.