Neurogenesis and development of the central nervous system in the embryo stage of swimming crabs, Portunus trituberculatus, were studied by the histological method. The brain appeared at the egg-nauplius stage Ⅱ and was composed of protocerebrum, deutocerebrum and tritocerebrum under microscope. The protocerebrum was composed of lamina ganglionaris, lateral protocerebrum and medial protocerebrum at the egg-zoea stage Ⅱ, and olfactory lobe appeared and arranged beside the esophagus with deutocerebrum and tritocerebrum. The ventral nerve cord of the crab in the embryo included 1 pair mandibular neuromere, 2 pairs neuromeres of maxillae, 2 pairs neuromeres of maxillipede and abdomen nerve cord. Under microscope, the mandibular neuromere appeared at the egg-nauplius stage Ⅱ, the neuromeres of maxillae and neuromeres of maxillipede appeared at the egg-zoea stage Ⅱ, and the abdomen nerve cord formed at the egg-zoea stage Ⅲ. The central nervous system was composed of brain and ventral nerve cord in the embryo stage of the swimming crab. The brain was composed of protocerebrum, deutocerebrum and tritocerebrum. The brain connected to the suboesophageal ganglia with circumoesophageal fibre. The forming time of the part of the central nervous system showed difference in the embryonic development.