The invention relates to a seaweed synergia compound fertilizer and a preparation method thereof. The method comprises the steps of: preparation of seaweed synergists, preparation of a granulating material, preparation of urea meltwater, granulation and the like. According to the fertilizer and the method, a fusing urea guniting process is combined with a drum granulating process to produce the seaweed synergia compound fertilizer, and due to the promotion effect of active ingredients in a seaweed synergia solution on crops during growth, the inhibiting effect of the active ingredients on soil urease, and the influence of the active ingredients on chemical valence bond features of urea, the crop yield is increased, the fertilizer utilization rate is increased, the nutrient loss is reduced, and the secondary pollution is avoided. The fertilizer product disclosed by the invention has the characteristics of being wide in material sources, free from deliquescing, convenient to deliver, apply and produce, simple in process, low in cost, beneficial to industrial generalization, and the like, and has a wide application prospect in production.