Objective: To explore a green and efficient method for extracting chitin. Methods: The crayfish shells were crushed through three mesh sieves to obtain the raw material. Utilizing ultrasonic wave and citric acid and urea to remove calcium and protein from the sample, decolorize it with hydrogen peroxide, filter it, and then dry it to produce chitin products. The particle size of the chitin sample was analyzed by laser scattering particle size distribution analyzer. Infrared absorption characteristics were measured by an infrared spectrometer. Scanning electron microscopy was used to observe the apparent structure of the sample. Results: It was shown that the larger the mesh size, the higher the purity of the chitin product. The yield of chitin from 200 mesh crayfish shell powder increased to 43.93%, and the purity increased to 55.39%. The particle size of chitin samples obtained from shrimp shell powder of three mesh numbers after plasma treatment decreased from 340.05, 184.30, and 137.39 μm without plasma treatment to 195.95, 159.02, and 53.51 μm respectively. Infrared spectrum analysis showed that the crayfish shell powder treated by plasma-assisted ultrasonic-assisted weak acid and weak base method displayed the absorption characteristics of chitin and magenta, indicating that the main component of the treated sample was chitin. The scanning electron microscope results showed that the structure of the chitin sample was looser and the surface was uneven after plasma treatment. Multiple statistical analyses showed that screening and plasma treatment had a significant impact on the whole properties of chitin samples. Conclusion: In this study, plasma and ultrasonic-assisted weak acid and weak base extraction of chitin from crayfish shells can improve the traditional acid-base process, reduce the environmental pollution of acid-base reagents, and effectively improve the extraction rate and purity of chitin.