Abstract: In this paper,the 5-day biochemical oxygen demand (BOD5) was measured by dilution inoculation method and differential pressure method. The experimental results show that both methods can be used to determine BOD5,but each has its own advantages and disadvantages. The dilution incubation method is almost suitable for any sample,but requires a longer experimental cycle and higher experimental skills. The pressure difference method,in comparison to the standard method,offers a simpler operation and improved consistency. It is particularly suitable for samples with higher BOD5 concentrations,albeit at a higher cost.