Sexual selection was referred to as the mate choice between males and females, and played an important role in the process of speciation and species evolution. The past two decades have seen extensive growth of sexual seletion researches. Though most of these researches were focused on terraneous animals, studies on aquatic animals were gradually increasing, especially for fishes, sea urchins, and oysters, etc. Unlike most of terraneous animals, the sexual selection of aquatic animals is original and conservative, for example, no perfect sense organs, no remarkable genitalia and nearly no parent behavior. However, through a long time evolution process, the mode of sexual selection in some aquatic animals is also unique. To summarize recent research results and enlighten novel research ideas of sexual selection, here, we have a review on hydrobios sexual selection. The sexual selection modes are various in aquatic animals, and change from individual to cell levels. Like high terraneous animals, there are conspicuous sexual dimorphism between male and female in some fishes, such as Xiphophorus helleri and Goodea atripinnis. Additionally, body color, body size and even aggressive reaction of males are all seletive objects for females in the mate choice. However, unlike terraneous animals, quite a number of sexual selection exist between sperms and eggs, such as sea urchins and oysters. The genes coding bindins and bindin receptors are high polymorphism in sea urchins, and it was believed that the polymorphism was the selection basis of eggs for sperms. Additionally, there is the phenomenon of sex role reverse in some fishes, such as pipefish and sea horse, which is similar to some insects. What is the mechanism of sexual selection in aquatic animals? At present, many researches have given stronger supports that the mating selections were mainly based on both of additive genetic benefits and nonadditive genetic benefits. It is worth noting though most of sexual selection is benefitial to the fitness of aquatic anmials, some mating choices are deleterious, for example, the males attracted to females yielded more low viability offspring than other males in Poecilia reticulata. So, the mechanism of sexual selection in aquatic animals is also complicated, which includes not only the single direction selection of female for male or male for female, but innersex competition. In this review, we also summarized the influence factors to sexual selection, which include the time and space of mate choice, human activity, other organism’s activity, the intensity and contrast of body color, predators, even adulterer, etc. Today, the existing sexual selection studies of aquatic animals mainly are focused on the fishes, sea urchins, and oysters, but little on the other aquatic animals. Thus, more studies are still needed in order to clarify the complicated behaviors and mechanisms of sexual selection in all kinds of hydrobios. The following problems are interesting for us to have further researches: (1) How do the sexual selection drive speciation of aquatic animals? (2) The genetic mechanism of diversity in sexual selection; (3) The relationship between nature selection and sexual selection; (4) The mechanism of female making choice; (5) The action of sexual selection in the germplasm protection. In addition, the classical theory of sexual selection is enduring new kind of trial, and new theory has been put forward in the fish, Symphodus tinca.