Objects retrieving, especially irregular shaped objects, using underwater ROVs (Remotely Operated Vehicles) are challenging. Traditional grabbing devices mounted on underwater ROV arms are not effective at grasping small and irregular shaped parts. To tackle this problem, this paper proposes a non-contact swirling suction cup based mechanical claw grasper designed for small underwater object retrieving. First, the overall structure of the robotic arm equipped with the mechanical claw grasper is introduced. Second, simulations examine the robotic arm’s claw grasper during underwater suction and gripping after activating the suction cup. Third, the performance of claw grasper equipped with negative pressure suction cups is compared to those with swirling suction cups. Simulation results show that the proposed robotic arm equipped with swirling suction cups can effectively perform underwater suction-based object grasping.