This paper deals with the embryonic development of A. gigas. Theembryonic development stages were discontinuously observed because of the egg-ca.psure. The mathod was the fixadate collected specimen and the egg-capsurebroken into spieces to draw out the embryo. In atmospheric temperature at 25土10C,the embryonic development took 274 hours and the length of embryo increased22 times. According to the external morphology,whole developmental course of theembryo can be divided into7 periods as follows:1 .Cleavage period In the early period cleavage follows the spiral molluscan pattern.The polar bodies mark the animal pole of the egg?2 .Blastula Period There is no morpholgycially dletinct ,but the blastula cayity cari been sean on the sectjceng epacimen 3 .Gastrula period Gastrula can be divided into the earlier stage,middle stageand last stage,but passed epiboly and invagination. 4 .Trochophore larva period The time is of short duration. The embryo hasapical,metatroch and telotroch. 5. Veliger larva period Nifty-two hours later the embryo has become a veli-ger larva with veliger area. The foot is bilobed, the larval shell has begun to besecreted. The adult tentacle primordia appear. 6. Juvenile snail form period The foot can move, eye primordia appear，theshell covers the body or visceral mass. The time is 60% of the embryonic develop-went. 7 .Hatching Just hatching juvenile snail has two whorl. The larval livercells appear to be red.