Abstract: The wastewater from aquaculture and aquatic products processing was complex, salty and difficult to be treated. The mixotrophic denitrification process was adopted in continuous stirred tank reactor(CSTR) for simultaneous removal of C and N. The acclimation of activated sludge at different salinity, and the effects of C/N and HRT on the synergistic/competitive transaction of autotrophic and heterotrophic denitrification in mixotrophic system were analyzed. Results showed that among the three acclimation methods of autotrophic/heterotrophic denitrification sludge, the acclimation efficiency was in the order of high salt > low salt-high salt > no salt-low salt-high salt. High salt acclimation method was beneficial for the rapid start-up of denitrification system. In the mixotrophic system, the removal load and removal rate of NO_2^- reached 0.3 kg/(m ³·d) and 99.7%, respectively, with HRT of 8.0 h. The removal rates of NO_2^- and COD reached 99.9% and 99.0%, respectively, with C/N of 5.0. Therefore, HRT of 8.0 h and C/N of 5.0 were more conducive to the high operating efficiency of mixotrophic denitrification system.