The severe global climate changes result in consecutive torrential rains in rainy season, and causes water loss and soil erosion. For an effective water and soil conservation, geotextiles are commonly used in geotechnical engineering. Geotextiles should able to isolate soil, filter water, and reinforce the soil; therefore, the material for geotextiles should be acid-resistant and alkali-resistant, such as polypropylene (PP) and polyester (PET). This study uses PP fibers as the skin and PET plied yarns as the core to form PP/PET composite tubular knits on a cord knitting machine. The PET plied yarn is fed with a specified tensile strength, and only the tooth number of the drive gear varies. Mechanical property test results show that a drive gear of 30 teeth increases the tensile strength of the resulting tubular knits; however, with a drive gear of 35 teeth, the tensile strength decreases. An optimal core coverage occurs with a drive gear of 30 teeth.