Abstract: With the rapid development of offshore aquaculture, the direct discharge of high-density aquaculture tail water has caused increasingly serious damage to the marine environment. Effective treatment of aquaculture tail water has become a top priority. At present, the treatment methods of high ammonia-nitrogen aquaculture tail water mainly include physical method, chemical method and biodegradation method. Among them, the physical and chemical treatment processes are complex, the equipment and operation costs are high, and it is easy to cause secondary pollution. Microbial remediation technology has become the first choice for tail water treatment because of its high efficiency and environmental protection. At present, numerous ammonia-nitrogen degrading bacterial strains have been documented, including autotrophs and heterotrophs. Among them, autotrophic nitrifying bacteria have been widely used in the process of ammonia-nitrogen degradation in aquaculture wastewater. However, due to the problems of long growth cycle and strict culture conditions of autotrophic nitrifying bacteria, more scholars have begun to pay attention to heterotrophic ammonia-nitrogen degrading bacteria with short growth cycle, high efficiency and robust adaptability in recent years. In addition, the complexity and salinity effects of mariculture tail water make it impossible for heterotrophic ammonia-nitrogen-degrading bacteria from general freshwater sources to exert good nitrogen removal performance. Therefore, in order to screen out high-efficiency ammonia-nitrogen degrading bacteria and apply them to the purification of aquaculture seawater to solve the problem of excessive ammonia-nitrogen caused by high-density aquaculture, a heterotrophic ammonia-nitrogen degrading bacteria was screened from natural seawater in this study. It was identified as Pseudomonas aeruginosa and named CH1. The preliminary test of its ammonia-nitrogen degradation ability showed that the bacteria could completely degrade ammonia-nitrogen with an initial concentration of 100 mg/L within 24 h, showing efficient ammonia-nitrogen degradation ability. Therefore, the degradation conditions of strain CH1 under high concentration of ammonia-nitrogen (1 100 mg/L) were further optimized by single factor control variable method and orthogonal test. The results showed that the degree of influence of various factors on the ammonia-nitrogen degradation efficiency of strain CH1 was C/N > pH > salinity > temperature, and the optimal degradation conditions were as follows: utilizing sodium citrate as carbon source, C/N ratio was 5, salinity was 15, temperature was 35 °C, pH was 8.0, and the maximum ammonia-nitrogen degradation efficiency was 45.53% ± 0.46%. After optimizing the culture conditions, the strain CH1 could tolerate up to 2 300 mg/L ammonia-nitrogen concentration. Studies have shown that strain CH1 has high ammonia-nitrogen degradation ability, wide environmental adaptability and strong salt tolerance (salinity≤ 25) compared with other ammonia-nitrogen degrading bacteria, and has broad application prospects in ammonia-nitrogen treatment of aquaculture seawater with different salinities. This study can provide candidate strains and theoretical guidance for the regulation of ammonia-nitrogen in aquaculture seawater.