The invention relates to a method for preparing a food condiment, i.e. a sea asparagus soup spice. Sea asparagus has obvious regulating effect on hypertension, hyperlipidemia, hypercholesterolemia and diabetes, has effect of reducing weight and can improve human immunity and prevent parkinsonism syndrome. In the prior art, a method for deep processing the sea asparagus comprises the steps of carrying out centrifugal dehydration and freeze drying to produce the dehydrated sea asparagus and then grinding the dehydrated sea asparagus to obtain sea asparagus plant salt, and has the defects that the nutritional ingredients in the sea asparagus cannot be dissolved completely; the utilization rate is low; and the product cost is high. The method for preparing the sea asparagus soup spice of the invention comprises the following steps: taking the fresh sea asparagus to carry out washing, juicing and spray drying, carrying out compounding on the obtained product, uniformly mixing the sea asparagus powder subjected to spray drying, salt, monosodium glutamate, pepper, ginger powder, white granulated sugar and xanthan gum; and weighing the mixture to package. The method of the invention has the advantages of simple production process, rich nutrition of the product, outstanding characteristics of sea vegetables, good dissolubility, easy adsorption, capability of preparing the soup spice with various tastes and suitable industrial production.