A set of trammel net for the capture of swimming crab Portunus trituberculatus was designed and tested in field experiments, based on the biological habit and body characteristics of the target species. The designed fishing gear has a principle dimensions of 50.00 m×1.08 m with a 50 m head rope and a 66 m bottom rope. The size of the one inner net suit is 1200 mesh×18.5 mesh with a mesh size of 120mm and that of the two outer net suits is 200 mesh×2.5 mesh with a mesh size of 500mm. From 4th to 26th September 2015, the designed fishing gear was used to catch swimming crab in Laizhou Bay. The CPUE of the designed net was 1.61kg/webbing and the mean body weight of swimming crabs caught was 175.69g. Swimming crab, as the main species of the catching, accounted for  99.31% of the total catch. The bottom of the net suits of the designed net is loose because the bottom rope is 32 percent longer than the head rope, and this characteristic improves the binding performance on the swimming crab and thus the catching rate. The bigger mesh size of the inner net suit and the lower height of the designed net increases the releasing rate of young fishes and reduces the catching of pelagic fishes, respectively. The low fish catching rate of the designed net is very beneficial for the protection of fishery resources.