Near-infrared spectroscopy has been widely used for the rapid analysis of the physical and chemical properties of straw, offering advantages such as fast detection speed, high efficiency, and non-destructive testing. However, in practical applications, differences in straw particle size can reduce the detection accuracy and stability of the model. For rice straw samples with varying geometric particle sizes, near-infrared spectra were obtained in the 10 000~4 000 cm^-1 wavelength range. Polynomial fitting (PF) was employed to remove background signals from the spectral data of the straw samples. A one-way analysis of variance (ANOVA) was used to perform statistical testing (P<0.05) on the spectral feature signals of the geometrically sized straw samples after polynomial fitting. Principal component analysis (PCA) and Biplot analysis were employed to assess the contribution of spectral feature signals to the spectral differences among straw samples with different geometric particle sizes. Pearson and Spearman correlation analyses were used to screen for key spectral feature signals. Based on the quadratic polynomial fitting mathematical model, it was assumed that absorbance was composed of particle size-related spectral information (PSRSI) and non-particle size-related spectral information (nPSRSI). A particle size regression correction method (PSRCM) was proposed based on the absorbance and particle size of key spectral feature signals. The results indicated that the spectral feature signals at 5 180 cm^-1 of the geometric particle size straw samples exhibited extremely significant differences (P≤0.05, P≤0.01, P≤0.001) and showed a highly significant correlation with particle size (Pearson's r was 0.96). The quadratic polynomial mathematical model performed optimally, with an average coefficient of determination R² and root mean square error (RMSE) of 0.53 and 0.002 1, respectively. PSRCM effectively corrected the spectral differences caused by characteristic signals at 6 824 cm^-1, 5 360 cm^-1, and 5 180 cm^-1, with correction effects significantly superior to those of standard normal variate transformation (SNV) and multiplicative scatter correction (MSC). The research result can provide a theoretical basis for the transfer correction method of straw near-infrared spectroscopy models, which can be applied without the need for standard samples.