In order to explore the PET fiber's potential as a filter medium to treat the water produced from oil production, modification technology was adopted to modify the fiber surface. After modification, the PET fiber surface was grafted by the -COOH, =NH and -OH groups. Therefore, the property of the modified fiber changed from oleophilic to hydrophilic, which makes the fiber easy to backwash. Water produced from atypical oil field in the north of China was treated on site with filter filled with this new fiber medium. The results are compared with the results from a filter filled with currently popular walnut medium, where the experiment conditions are the same as that of the fiber filter. When the velocity is lower than 15 m/h, the effluent from fiber filter can control the oil concentration < 2.4 mg/l, SS < 2.0 mg/l, and D50 < 2 microm, which meets the requirements for waterflood (water injection) into the ground. But the walnut medium filter can only control the oil concentration < 5 mg/l, TSS < 2.0 mg/l, and failed to control the d50 < 2 microm, which is the crucial deficiency of the walnut medium. The fiber medium still shows a great ability to control particles even with higher filtration velocity and worse influent. With a filtration velocity of 20 m/h and 36.4 microm d50 of influent, the d50 of the fiber filter effluent is 3.302 microm, but that of walnut filter is 10.74 microm. The reason for this is due to the compressibiliy of the fiber medium while the walnut median is incompressible. Recommendations for future studies on pilot-scale experiments to improve backwash and to determine operational parameters are presented.