The invention discloses a method of sewage water recycling in seaweed chemical industry production, the steps of which include that pre-treating sodium alginate crude liquid gum, checking the capacity of alginic acid in the pre-treated liquid gum and adding corresponding weight of calcium chloride according to the capacity of alginic acid to precipitate out calcium alginate sufficiently, collecting the separated supernatant fluid and the sewage water formed in the process of generation, checking the capacity of calcium chloride and adding corresponding weight of water treatment agent which can deposit all calcium ions, displaying still for one night and separating out the supernatant fluid, which replaces tap water to be directly used for the dilution of next sodium alginate crude liquid gum; the separated supernatant fluid can be reciprocally used according to the method of the invention. The manufacturing technique of the invention can reduce the discharging capacity of the seaweed chemical industry sewage water at 80% or more, further, the invention not only doesn't influence the volume of production and the quality of the chemical product, but also creates remarkable economic benefit, still achieves distinct social benefit and ecological benefit.