The amphibiotic mollusca Onchidiidae are ideal species for the study of evolution from sea to land in marine invertebrates. In this paper, we choose three representative species of Onchidiidae, Paraoncidium reevesii, Onchidium struma and Platevindex mortoni, which live in shallow water, intertidal zone and supratidal zone respectively. We speculate that, with the change of habitats, the structure of their skin which has the function of respiration must have differences. Therefore, we observe the skin microstructure of three species via paraffin section and hematoxylin-eosin staining and also compare the skin parameters via JMP10.0 statisticalSsoftware. The results showed that, the basic structures of skin are almost the same among three species, which are made up of cuticular membrane, epidermis and dermis. Cuticular membrane covers on the surface of the skin, which is made up of protein. Dermis was composed of stratum spongiosum and stratum compactum. The stratum spongiosum abounded with two types of glands: mucus gland and granular gland. However, there were interspecific differences which include skin thickness, the number and the size of glands and so on. After the comparison between the structural difference and habitat environment, we concluded that O. struma, which mainly lives on terrestrial habitats, has a higher degree of keratinization and a larger number of glandular glands. Compared to O. struma, the mainly aquatic species P. reevesii has a thinner stratum comeum, while its number of mucus gland is the highest. As for the amphibian P. mortoni, the keratinizational degree of its skin is the medium and two kinds of glands are also not developed well. These results reflect three different ecological adaptive mechanisms and also provide the morphological basis for deeper research about the evolution of marine invertebrate from sea to land.