Abstract: Simulation test of water hyacinth (Eichhornia crassipes) for the purification of petroleum wastwater was conducted in two connected ponds. Results showed that in the warm months, the hyacinth ponds had strong ability for purifying the wastewater, and resulted in a much greater purification efficiency than traditional oxidation ponds. This purifying system with total detention time of 8 days could treat the wastewater to meet the water quality standards. The COD removal constants (K) of pond Ⅰ and pond Ⅱ were 0.376 and 0.151, the surface purification rates (Ps) were 9.51 and 2.38 gCOD/m2d, and the increases of biomass (wet weight) of water hyacinths were 226 and 210 g/m2d, respectively. The COD removal rate (R) decreased as the daily mean air temperature (T) decreased according to the formula: R=87.701 nT—200.15(10—24℃). Based on the experimental results, the calculation methods and parameters of the water hyacinth pond purifying system for the treatment of the Yan-Shan petrochemical wastewater are expounded.