The invention relates to a foaming method for biodegradable starch-based foamed plastic. The foaming method for the biodegradable starch-based foamed plastic comprises the following steps: (1) weighing biodegradable starch-based foamed plastic comprising the following components: 30-90 parts of starch, 10-50 parts of starch and acrylate grafted polymer and 0.1-40 parts of acrylate homopolymer; (2) selecting water as a foaming agent; (3) selecting 0.5-2 parts of talcum powder as a nucleating agent; and (4) uniformly mixing materials obtained in the steps (1)-(3), and extruding by virtue of an extruding machine. The biodegradable starch-based foamed plastic product is better than domestic similar products in the aspects of operational performance, biodegradability and price respectively; meanwhile, the product can be completely decomposed and rapidly absorbed by microorganisms in soil after being used for multiple times, produces no pollution to the environment and has good environmental benefit and a broad application prospect; and research and development of the product have positive meaning on alleviation of 'white pollution' and scarcity of oil resources.