In this paper, we used the S450 near-infrared high-density grating spectrometer with technology of high-speed acquisition developed by Shanghai Lengguang Technology Co., Ltd. and China Agricultural University, took wheat and tobacco as the experimental object, and aimed at the high-density spectra (wavelength range is 900~ 2500nm, interval of wavelength is 0.1 nm, contains 16 001 data points). By adapting processing methods such as S.G. (Savitzky-Golay) smooth, FCMWS (Fixed window combine moved window smoothing) and the First Derivative, Partial Least Squares (PLS) was also used to model and predict the content of crude protein in wheat, nicotine and total sugar in tobacco, evaluate performance of the spectrometer, and optimize the parameters of processing methods. The results show that: (1) The performance of the models was greatly improved after the high density spectrum was processed by S.G. and the first derivative. Optimizing the parameter M (fitting order) and N(number of smoothing point) , if M is a fixed number, N can be selected from a wider range, and when M=2, N is in the interval of 201~801, the performance of models is ideal and stable; (2) The FCMWS was designed for smoothing layers of two, fixed window size of the first layer K1 and second layer K2 , and it was concluded that the performance of models is better and superior when the multiplication of K1 and K2 is about 150~310, moreover the FCMWS algorithm is speedy in modeling. (3) In order to analyze instrument differences, only took wheat as the object, which was measured by two S450 spectrometers, experimentally, whether the spectrum is processed by S.G. or FCMWS, the relative deviation of the predicted data from different models between instruments is less than 2.00%, which is far lower than the relative deviation between the predicted and reference values. It indicates that the above two methods can reduce the instrument differences and models can transfer stably among instruments. For wheat, tobacco and other agricultural products, the results of this study reflect that the domestic high-density grating spectrometer S450 combined with de-noising methods, can meet the actual requirements of quality detection and model transfer, and the grating instrument is relatively low-cost, which is significant for popularizing application of the rapid detection technology of near infrared in the agricultural field.