The invention discloses an undersea suction anchor which comprises a main drum, a top face of the main barrel is sealed, a lower end of the main barrel is opened, and a main barrel drainage hole is arranged on the top face of the main drum. The undersea suction anchor is characterized in that a barrel skirt is movably sleeved on the main drum, the barrel skirt comprises a horizontal top face and a barrel-shaped lateral wall, a barrel skirt drainage hole is formed in the horizontal top face of the barrel skirt, a telescopic hook locating the barrel skirt at the upper portion of the main barrel is arranged on the barrel-shaped lateral wall at the upper portion of the main barrel, an anchor ring concentric with the main barrel is arranged at the upper end of the main barrel, anchor branches are evenly arranged on the anchor ring, one ends of the anchor branches are hinged to the anchor ring, and the other ends of the anchor branches are hinged to the barrel skirt through inclined support rods. The whole vertical section of the suction anchor is in an umbrella shape, in the sinking process of the anchor body, along with landing-on-seabed of the barrel skirt, the anchor branches are driven by the inclined support rods to be gradually opened, and after the main barrel sinking is finished, the anchor branches cling to the surface of the seabed in a horizontal extending mode. The undersea suction anchor can improve the integral stability of the suction anchor, increases pulling resistance and horizontal bearing force, and reinforces wave-corrosion-resistance performance.