A denitrifying strain ZY04 with high nitrite-accumulating rate was isolated and purified from activated sludge in lab-scale A²/O reactor. The strain was characterized and identified as Acinetobacter johnsonii by 16S rDNA phylogenetic analysis. The Logistic model were fitted well to the experimental growth curve of strain ZY04 with the growth equation constants of a=0.6588, b=24.08, k=0.2413. To investigate the partial denitrification performance of strain ZY04, the batch experiments were conducted by fixing the initial concentration at 100mg/L and supplying with different quantities of sodium acetate to control the carbon-nitrogen ratio (TOC/TN) at 3.5, 4.5, 5.5, 6.5. The result showed that ZY04 exhibited the high removal rate of nitrate over 95% under different TOC/TN conditions. The nitrite accumulation rate reached over 70% within 17 hours under the TOC/TN at 3.5 and 4.5, while the rate was over 85% within 11hours under the condition with the TOC/TN at 5.5 and 6.5. the highest nitrite accumulation rate was up to 91% when the TOC/TN was set as 5.5. The results of inhibitory kinetics analysis revealed that three biokinetic models (Aiba, Edwards and Andrews) could well simulate the growth pattern of strain ZY04inhibited by single substrate (nitrate or sodium acetate). In the double-substrate inhibitory model, six models of nine combinations successfully fitted the growth characteristic of strain affected by double substrate of nitrate and sodium acetate. The relevant semi-saturation parameters and substrate inhibition parameters were obtained, and the correlation coefficient (R²) could reach 98%.