The population growth, reproduction and survival rates of a rotifer (Brachionus urceolaris) population were studied in growth media over a range of pH-values (pH 7-10) and different concentrations of un-ionized ammonia (NH3-N:0.5、1、2、5 and 10mg/L). The results that in the absence of un-ionized ammonia, the rotifers could survive across the entire pH range(pH 7-10). Both the population net reproductive rate and the intrinsic growth rate were highest at pH 7, but the generation time was longest at pH 8. While at a favorable range of pH (pH 7、8) and at a concentration of NH3-N below 2mg/L, the age-specific survivorship curve and population growth rates similar to the control. At a concentration of 5mg NH3-N/L, the age-specific survivorship decreased and the population growth rate a lot declined. Under the 10mg NH3-N/L concentration, the individuals died in 48-72h, carrying no egg. When exposed to un-ionized ammonia at an unfavorable pH, the population′s intrinsic growth rate was negative, its reproductive output dropped and the population declined. The above results indicate that a combination of high pH and high concentration of un-ionized ammonia has a clear negative effect on growth and survival of the rotifer, B. urceolaris.