The invention relates to the field of bacteriostats, and concretely relates to a seaweed endophytic fungus-derived natural indocyano alkaloid compound, a preparation method thereof, and an applicationthereof in bacteriostasis. The specific structural formula of the compound is represented by formula (I). The preparation method comprises the following steps: inoculating a fungal culture medium with the seaweed endophytic fungus Aspergillus versicolor DL-29, carrying out fermentation culturing, and separating and purifying the obtained fermentation product to obtain the indocyano alkaloid compound of the formula (I). Bacteriostatic activity experiments of the alkaloid compound show that the diameter of the inhibition zone of the compound at 30 [mu]g/tablet is 7 mm.