The main function of both cod liver oil and vitamin D3 is to promote calcium absorption, which is beneficial to human growth and development. Cod liver oil is a vitamin drug, the components are vitamin A, vitamin D. It is commonly used in the treatment of rickets, night blindness, pediatric tetany, as well as the prevention and treatment of vitamin AD deficiency. Vitamin A and vitamin D are essential substances for human growth and development. Vitamin A can be converted to retinaldehyde in the human body, which is involved in the synthesis of the photoreceptor retinal, in order to maintain the process of visual dark adaptation and increase the photoreceptor performance of the retina, as well as play an important role in the growth of bones and the development of the gonads. Vitamin D can promote the absorption of calcium and phosphorus in the intestinal tract, decalcify old bone and calcify new bone, and enhance the reabsorption of calcium and phosphorus by renal tubular cells, thus regulating serum calcium and phosphorus concentrations. It is especially important for the development of fetus, infants and young children, such as the integrity of epithelial tissues, vision, reproductive organs, blood calcium and phosphorus constancy, as well as the growth and development of bones and teeth. Vitamin D3 is composed of only D3, and its main function is that it can improve the body’s ability to absorb the elements of calcium and phosphorus, and it can promote bone growth and bone calcification. To a certain extent, it can effectively maintain the normal level of citrate in the blood, and effectively prevent rickets, hand and foot twitching and so on. During the period of taking vitamin D3, it is recommended to sunbathe frequently, and it is necessary to strengthen the nutrition in the diet, ensure enough milk, and add the appropriate complementary food according to the age group to avoid vitamin D3 deficiency. Usually, the purpose of taking cod liver oil and D3 is to supplement vitamin D, so it is sufficient to choose one of these medications. If there are symptoms of calcium deficiency or vitamin D deficiency, attention should be paid to timely supplementation, so as not to affect the growth and development of the body.