Abstract: This paper describes the development and characteristics changes in the brain of grass carp and the position changes of the brain in the cranial cavity from hatching to 500 mm total length(TL). The general structure of the well-developed brain has been described in detail. The characteristics tend to stability when the brain becomes well-development after 125mm TL. The brain contacts the cranial cavity tightly and the only space is ahead of the telencephalon before 50 mm TL. The position of the brain gradually moves to the posterior part of the cavity. The brain is on the latter half of the cranial cavity after 227 mm TL. The morphology and the position changes of the paraphysis, epiphysis, hypophysis and the vascular sac have also been described.