The body color of swimming crab varies with the surrounding environment. Individuals living in the sand bottom have a light gray-green head breastplate with a round white spot in the front gill area. Most of the claw feet are purple-red with white spots, and some or all of their ventral surfaces are white. The long joints and wrist joints of the first three pairs of feet are also white, the palms are blue-white, the fur is brown, the knuckles are purple-blue or purple-red, and the fourth pair of feet are green with white spots, with purple-blue fingers. Individuals living among seaweed are darker in color. For omnivorous, fish, shrimp, shellfish, algae all eat, and even eat the same kind, like to eat animal carcasses.
The head breastplate is spindle-shaped and slightly raised. There are three prominent verrucous bulges on the surface, 1 in the stomach area and 2 in the heart area. Its shape is like an ellipse, with sharp ends like weaving shuttles, so it has the name of Portunus trituberculatus. Each of the two front side edges has nine serrations, and the ninth serration is particularly long and extends to the left and right. Frontal margin has 4 small teeth. There are 1 pairs of rotatable compound eyes with handles on both sides of the forehead.
There are five pairs of breasts and feet. The sting foot is developed, the long section is prismatic, and the inner edge has blunt teeth. The knuckles of the fourth pair of walking feet are flat, wide and as thin as paddles, suitable for swimming. The abdomen is flat (commonly known as crab navel), the abdomen of male crab is triangular, and that of female crab is round. The back of the male crab is dark green, the female crab is purple, and the ventral surface is gray.