The invention relates to a spirogyra sustained-release inhibitor containing a cinnamomum camphora extract and a preparation method thereof. The inhibitor comprises the following components by weight percentage: 50-70% of polylactic acid, 20-30% of the cinnamomum camphora extract, 1-10% of ethoxylated fatty acid methyl ester, 1-10% of sodium carbonate and 8-30% of hectorite powder. The sustained-release inhibitor can achieve a spirogyra removal rate up to 70% or above, has long action time and an effective time of 7-15d, guarantees the effect concentration and effect time of spirogyra outbreakarea, and can achieve more thorough elimination of nearshore spirogyra; the raw material sources are wide, the components are basically degradable and non-toxic materials, the sustained-release inhibitor does not destroy the original aquatic ecosystem, has high safety, is free of nitrogen, phosphorus and other nutrients and pigment components causing water yellowing, and does not cause secondary pollution to water quality and landscapes.