Abstract: Abstract: China is a traditional agricultural country, and the output of all kinds of crops straw in China has more than 7 tons according to some related statistics. As a kind of solid biomass waste, and also a kind of renewable resource, the comprehensive utilization rate of this material is not very high in China. In order to analyze the relationship between microscopic structure and macroscopic mechanical properties of wheat straw/polypropylene (PP) composites during aging experiments, AMT (angle measure technique) method was introduced to investigate scale spectra of scanning electronic microscope (SEM) images of surface microstructure of wheat straw/ PP composites at different aging periods in this study. With wheat straw powder as filler and polypropylene plastic film as matrix, wheat straw/PP composites were prepared by using compound mold pressing method. Accelerated UV aging test with xenon lamp was completed, and macroscopic mechanics properties of the composites were tested before and after aging. The microscopic surface morphology changes of the composites were observed using SEM at different aging period and the typical SEM images were taken simultaneously. After several necessary images preprocessing for SEM images, through AMT method the mean angle (MA) spectra of SEM images of the composites were derived, the changing relationships with the growing aging periods between characteristic angle & characteristic scale of spectra of composites and their macroscopic mechanics properties were analyzed as well. The results showed that with the increasing of aging periods mechanical properties of composites were on the decline as a whole, while characteristic angle & characteristic scale of MA spectra of them tended to increase overall. It was proved that there were significant or extremely significant correlations between characteristic angle & characteristic scale of microstructure image of composites and their macroscopic mechanics properties by using correlation analysis, especially the correlation coefficient between characteristic angle and flexural strength was significantly, which was -0.975. By using principal component analysis (PCA) the validity and discriminability of AMT method has been proved, differences of MA spectra of composites at different aging period can be described well by principal component 1 only. Unlike FFT (fast Fourier transform) and wavelet analysis, AMT methods is a thoroughly novel application of signal analysis in the measurement signal series, which can transforms the original signal domain to a very brand-new domain that is scale domain transform. It was verified that AMT method can well quantitative delineate the image texture of surface microstructure of the composite in this study. The works from our and other researchers have shown that AMT is capable of delivering very exact and discriminating characterizations of apparent features when confronted in description of texture complexity of digital images. AMT method has great values in quantitative delineating and analysis of complexity of measure series and image texture, so it can be expected that this approach will has wide employments and deep development in the future.