The present invention relates to a production method for a seaweed bio-composite organic liquid fertilizer. The method comprises the following steps: carrying out crushing grinding on fresh kelps; adding the crushed kelp slurry to a fermentation tank, and adding water; adjusting the pH value to 6.8-8.8, adding a composite enzyme and a microbial fermentation bacteria agent, uniformly stirring, and heating to a temperature of 25-60 DEG C, wherein the thermal insulation fermentation time is at least 85 hours; and filtering, and adding an acid production bacterial agent to obtain the seaweed bio-composite organic liquid fertilizer. According to the present invention, the water used in the method adopting the fresh kelps as the raw material to produce the product is saved by 90% compared with the method adopting the dried kelp raw material to produce the product; the energy is saved by 40% by adopting solar heating and thermal insulation fermentation production, the production cost can be reduced by 25%, and characteristics of energy saving, water saving, low carbon and environmental protection are provided; the seaweed bio-composite organic liquid fertilizer of the present invention has effects of combination of organic fertilizer, inorganic fertilizer, microbial fertilizer, and medium and trace element fertilizer, rapid acting, long lasting time, synergy, fertilizer retention, water retention, cold resistance, insect repelling, disease resistance, soil improving, and the like.