The invention discloses an automatic extracting method of carrageenan. According to the automatic extracting method, carrageenan is obtained via smashing, alkali treatment, water washing, gum cooking, filtering, salting out precipitating, press filtering, strip cutting, and crushing of seaweed. The automatic method comprises following steps: seaweed raw material is delivered into a raw material tank, and is delivered through a material smashing device, an alkali treatment device, a gum cooking device, a first frame and plate filtration machine, a second frame and plate filtration machine, a filter press, a strip cutting device, and a pulverizer successively. In a production line, the material smashing device is arranged on the upper part of the alkali treatment device, so that the raw material obtained via smashing in the material smashing device is delivered into the alkali treatment device under gravity effect, energy consumption and labor intensity are reduced, and high efficiency production and environment protection are realized.