This study designs a rope-net spreading device for kelp with a cover net, aiming to reduce labor intensity during the spreading process and improve the drying quality of kelp. The overall structure of the device includes a wire rope synchronous anti-slip device, a rope net assembly, a tail drum assembly, a double roller bracket assembly, and a cover net assembly. Through pilot-scale testing, the 50-meter-long continuous conveying and spreading equipment for seaweed rope nets was evaluated under mass loads ranging from 20 kg to 100 kg. A trend formula between the distributed load and the dragging tension of the steel wire rope was derived as y = 2.8984x + 778.46. With the relative displacement of the steel wire rope controlled within ±4 mm, the covering net can withstand a maximum wind speed of 13.8 m/s. These results provide a basis for determining the dragging force and power configuration of spreading equipment of different lengths. Furthermore, by employing synchronous conveying of the steel wire rope net belt and coordinated constant-tension deployment of the covering net, continuous, efficient, and uniform spreading of seaweed was achieved. This approach effectively prevents wind interference with the net-spread seaweed, avoids seaweed being blown to the ground, ensures cleanliness, and improves drying quality. The flatness and drying speed of the spread dried seaweed are superior to those achieved by vertical hanging.