Abstract: We observed the embryonic development of Tylorrhynchus heterochaeta and investigated the effect of salinity on their fertilization and hatching rate. In an artificial incubation experiment, the fertilized eggs were hatched in six groups (each group with 3 parallels) at different salinities (A:0, B:5, C:10, D:13, E:15, F:20). The results show:1) The embryonic development of T.heterochaeta could be divided into eight stages, including zygote, cleavage, blastula, gastrula, early trochophore, late trochophore, three setiger nectochaete (unhatch) and three setiger nectochaete (hatch). 2) The hatching rate was significantly affected by different salinities. The highest fertilization and hatching rate were observed in Group C, significantly different from those in the other groups(P < 0.05). The suitable salinity range for the fertilization was 10~13, and the optimum hatching salinity was 10.