In order to study the effects of replacement of soybean oil (SO) with black soldier fly larvae oil (BSO) in grass carp production practice, five isolipidic and isonitrogen experimental diets were formulated by replacing 0% (SO), 25% (BSO25), 50% (BSO50), 75% (BSO75) and 100% (BSO100) of SO with BSO, respectively. After 56 days of feeding, the changes of growth performance, body composition, serum biochemical indexes, antioxidant capacity, intestinal and liver tissue structure, and intestinal microbiota of grass carp were detected. The results showed that there were no significant differences in WGR, FCR, SGR, VSI, CF and HSI among the treatment groups. Compared with the SO group, the activity of serum superoxide dismutase (SOD) in BSO25 and BSO50 groups was significantly higher, malondialdehyde (MDA) activity in BSO75 and BSO100 groups was significantly decreased, and the catalase (CAT) activity was significantly increased in BSO50, BS075 and BSFO100 groups. The morphology of liver cells in BSO100 group was mostly of irregular shape, with unclear boundaries between cells. The enzyme activity of AST, ALT and LDL-C in serum was significantly higher than that of SO group. The community diversity indexes Sobs, Shannon and the richness indexes Chao, Ace in the BSO100 group were significantly higher than those in the SO group. The results showed that 100% soybean oil replaced by BSO did not affect the growth of grass carp, and it could enhance the antioxidant capacity and the abundance and diversity of intestinal microbiota. However, in group BSO100, the liver was damaged, and long-term feeding will have an adverse effect on the body. Therefore, in the feed, BSO should not completely replace soybean oil. It is suggested that the replacement ratio should not exceed 75%.