In the process of shield TBM construction, an annular gap will be formed between the surrounding rock and the segment, and pea gravel is the main material to fill the annular gap. It is of great significance to carry out quantitative research on the morphological characteristics of pea gravel for its material properties. The test is carried out with four kinds of pea gravel samples, including artificial gravel and natural pebble, combined with digital image analysis and particle size analysis. To analyze the test results, six quantitative indicators of particle morphology from three aspects of the contour shape, angular shape, and particle size were firstly obtained, and then the quantitative indexes were used to describe the morphological characteristics of the pea gravel samples. Finally, the image analysis results and the particle size analysis results were compared to verify the reliability of the image analysis results. The research results show that with the help of digital image analysis, the quantitative indexes of the morphological characteristics of pea gravel can be obtained quickly and effectively, which provides a basis for the screening and quality control of pea gravel in TBM constructed project.