The composition and function of intracapsular biochemical substances are intrinsically correlated; thus, it is important to quantify intracapsular nutritional composition, including protein, glycogen and lipid content, which are required for embryonic development. To explore the intracapsular fluid nutritional composition of the marine gastropod Hemifusus tuba Gmelin during early developmental stages, the embryonic development was divided into seven stages: fertilized egg, cleavage, morula, blastula, gastrula, veliger and juvenile. Results showed that the amino acids contents ranged from 44.98 to 71.52/100 g. Furthermore, 13 amino acids were identified, including five essential amino acids and eight non-essential amino acids. The contents of aspartic acid, proline, and valine were higher, while the contents of the other ten amino acids were relatively lower. Notably, aspartic acid and proline content varied across embryonic development. In addition, saturated fatty acids (SFAs) were dominant fatty acid components in the intracapsular fluid, in which C18:0 was the main fatty acid. Monounsaturated fatty acids (MUFA) primarily comprised C20:1(n − 9), accounting for 30% of the total fatty acids. At the same time, the content of C18:2(n − 6) decreased significantly from the fertilized egg to the blastula stage (p < 0.05). The content of C20:4(n − 6) from fertilized egg to gastrula stage was significantly reduced (p < 0.05). C22:6(n − 3) was significantly lower in the gastrula than in other stages (p < 0.05). Overall, this study provides new information on the intracapsular fluid nutritional composition of H. tuba, helping enrich the biological knowledge of the early developmental stages of marine gastropods.