Population dynamics and sexual reproduction of Moina irrasa were studied under four temperatures (15, 20, 25, 30℃) and food concentrations of 4×10⁵ cells/ml. The results showed that population density of M. irrasa presented a trend of gradual increase at first stage and decreased after it reached the density peak under four temperatures. With the increase of temperature, mature time, first reproduction time and the time reaching maximal population density declined, while body length of mother at mature and first off spring-produced decreased. In addition, the maximal population density of M. irrasa increased with increasing temperatures except 30℃. Mean maximal population densities of Moina irrasa were 882 ± 136ind./(200ml), 1351 ± 141 ind./(200ml), 1643 ± 105ind./(200ml), 1226 ± 82ind./(200ml) under four temperatures, respectively. The males and ephippia of M. irrasa were observed in all experimental groups, and male density increased with the incease of population density. The maximal male density and accumulative number of ephippia of M. irrasa occurred at 25℃, i. e. 169ind./(200ml) and 1444ind./(200ml). Relationship between temperature and the number of ephippia of M. irrasa was observed. Our results suggested that extreme temperature was not good for population growth of M. irrasa, and the formation of ephippia of M. irrasa was affected by temperature, food and population density together.