Abstract: Through the simulation and calculation of object Petri net modeling and simulation environment (OPMSE) for the emission mass concentrations of COD， BOD₅ and NH₃-N in waste water from paper-making industry， the range of COD， BOD₅ and NH₃-N mass concentrations in typical paper-making industry were inquiried and investigated in Qinghe basin. The results show that when the confidence level is 99%， the confidence interval of COD is (34.09， 41.84)， the confidence interval of BOD₅ is (6.65， 8.40)， and the confidence interval of NH₃-N is (6.28， 7.34). The mass concentration of the optimum effluent is ρ(COD)=12. 79mg/L， ρ(BOD₅)=2.62mg/L， ρ(NH₃-N)=3. 33mg/L， while the mass concentrations of the worst effluent are ρ(COD)=70.47mg/L， ρ(BOD₅)=14.51mg/L， ρ(NH₃-N)=10.22mg/L. Then making a comparison between the emission standards and simulation results are got. The direct emission limits of the paper-making industry are ρ(COD)=45mg/L， ρ(BOD₅)=9mg/L， ρ(NH₃-N)=8mg/L.

Key words: best available technology (BAT), emission limits, paper-making industry, simulation, Petri net