Abstract: The study aims to explore water absorption properties of castor inbred seeds and the effects of different parts of the seed on germination. The results showed that inbred lines had different water absorption capacities, and the capacity changed most quickly in the first 24 hours, then increased slowly, caruncle deletion played a lifting role in the process of water absorption of seed. The coefficient of volume and seed water absorption capacity was 0.5006 in case of caruncle, while the coefficient of volume and seed water absorption capacity was 0.6946 in case of caruncle deletion. Water absorption rate of inbred capsule husk ranged between 33%-380%. The test screened out 7 varieties of fast water absorption and slow dehydration. Water absorption rate of caruncle in vitro was negatively correlated with hundred-grain weight, the correlation coefficient was - 0.21307; and was negatively correlated with the weight of caruncle itself, the correlation coefficient was -0.6089. Thus, the author inferred that seed and caruncle with relatively small weight had strong water absorption capacity during germination. Germination test results indicated that the germination rate of seed with caruncle was lower than that of the seed without caruncle, and caruncle had obvious regulating effect on water absorption in germination.