The invention discloses an offshore barrel-shaped foundation for automatic liquefaction prevention and a construction method thereof. The offshore barrel-shaped foundation comprises a foundation bodyand an automatic liquefaction preventing system; the offshore barrel-shaped foundation body comprises an outer barrel, a drainage plate, an inner barrel, a split bolt and a drainage plate sealing topcover; the automatic liquefaction preventing system comprises a hole water pressure sensor, a drainage pipe joint, a sensor joint panel, an acquirer, an alarm and a water pump; and when an ultra-static hole water pressure, acquired by the acquirer, in a seabed around the offshore barrel-shaped foundation exceeds a seabed liquefaction prewarning value, the alarm gives out an alarm, the water pump is automatically started for water pumping, the hole water pressure in a seabed soil body around the offshore barrel-shaped foundation is reduced in time, and the seabed liquefaction risk is removed. Asuction cylinder technology is adopted, and the offshore barrel-shaped foundation is mounted without excavation and sinking, and is directly formed in the seabed or a riverbed, so that quick and safeconstruction of the offshore barrel-shaped foundation is realized, and the construction cost and the construction period are saved.