The body color of swimming crab changes with the change of surrounding environment. Individuals living in the sand bottom have a light gray-green head breastplate and a round white spot in the anterior branchial area. Most paws are purplish 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 and white, the fur is brown, the knuckles are purple-blue or purple-red, the fourth pair of feet is green with white spots, and the fingers are purple-blue. Individuals living in seaweed are darker in color. For omnivorous, fish, shrimp, shellfish, algae all eat, even eat the same kind, like to eat animal carcasses.
The head breastplate is spindle-shaped and slightly convex. There are three prominent verrucous bulges on the surface, stomach area 1 and heart area 2. Its shape is like an ellipse, and its two ends are pointed like weaving shuttles, so it has the name of Portunus trituberculatus. Each of the two front sides has nine serrations, and the ninth serration is particularly long and extends to the left and right. There are four small teeth on the forehead. There are 1 double rotatable compound eyes with handles on both sides of the forehead.
There are five pairs of breasts and feet. The thorn foot is developed, with long prismatic joints and blunt teeth on the inner edge. 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 the abdomen of female crab is round. The back of the male crab is dark green, the female crab is purple, and the abdomen is gray.