The factors affecting the effect of polyethylenepolyamine water clarifier produced by crosslinking linear ethylene oxide and propylene oxide with tetraethylene pentamine were studied experimentally. The results showed that the clear water process of this type of water clarifier was a demulsification process. When the temperature was higher than a certain value，the clear water effect of the water clarifier with relative molecular weight of about 10000 was mainly relative to the cloud point of the agent. When the temperature was higher than the cloud point temperature，the clear water effect became significantly worse. The cloud point temperature of the agent was mainly affected by the ratio of ethylene oxide to propylene oxide. The cloud point temperature of the agent increased with the increase of the ratio of ethylene oxide to propylene oxide. Therefore，the applicable temperature range of the water clarifier could be expanded by increasing the ratio of ethylene oxide to propylene oxide. By reducing the effective content of the water clarifier，the cloud point temperature could also be increased，so as to expand the applicable temperature range of the reagent. The injection test of water clarifier Q-03 and Q-03（diluted by 11%）with the ratio of ethylene oxide to propylene oxide of 5∶2 was carried out in the oil field. When the injection concentration was 200 mg/L，the effect of Q-03（11%）was significantly better than Q-03，which greatly improved the sewage treatment effect in the oil field.