The invention discloses degradable plastic based on plant fiber starch as well as a preparation method and preparation system of the degradable plastic. The degradable plastic comprises the following raw materials of: rice straw, straw, cassava starch, absolute ethyl alcohol, deionized water, natural resin powder, bamboo fiber powder, seaweed gel powder, a degradation accelerant, a modified treatment material, a filling agent, a cross-linking agent, polylactic acid, biological enzyme, a dispersing agent, a plasticizer and an antioxidant. The invention belongs to the technical field of degradable plastics. According to the degradable plastic based on the plant fiber starch and the preparation method of the degradable plastic, the use safety of a plastic product can be improved by using the plant fibers as the raw materials, the raw materials have certain environmental friendliness and reproducibility, the plant fibers have excellent biodegradability; and polylactic acid is added, the polylactic acid is a polymer obtained by polymerizing lactic acid serving as a main raw material, the raw material is sufficient in source and can be regenerated, and the production process of the polylactic acid is pollution-free.