Delaying skin-aging through diet is a hot research topic in recent years, but the anti-aging effects of fish gelatin and related mechanisms are not well understood. In this study, we prepared edible fish gelatin from the swim bladder of Cynoscion acoupa using three different processing methods, namely dried (DCM), soaked (SCM) and instanted (ICM), to investigate its anti-aging effects and mechanisms on D-galactose induced skin aging in mice, as well as its effects on the gut microbiota. The results demonstrated that fish gelatin significantly increased water content, collagen, hyaluronic acid (HA and hyaluronic acid (HYP content, and skin integrity of mice skin, as well as enhanced the antioxidative ability and anti-inflammatory capacity of the skin. In terms of protein and mRNA expression levels in skin tissue, CMs treated with different treatments can up-regulate the expression of EGFR and TIMP1, down-regulating the expression of MMP1 and MMP3, and increase the expression of COL3A1 and COL1A2. CMs attenuated the D-galactose-mediated inhibition collagen expression by stimulating the TGF-β/Smad signaling pathway, thereby maintaining collagen matrix homeostasis. In addition, we revealed that CMs reversed gut micribiota by increase the abundance of intestinal flora. In conclusion, we demonstrated that CMs, especially for ICM, as an effective dietary supplement, have potential anti-aging and skin health benefits.