Reinforced materials in polymer composite are usually fiber, yam and fabric. Fabrics used as reinforced materials include woven fabric, knitting fabric and braided fabric composed of different yams such as: glass, carbon, aramid, polyester, and polyamide yams. Of the above fabrics, woven fabric was widely used. Fabric's parameters influencing on its mechanical properties include: weaving pattern, warp density, weft density, warp count, weft count, surface weight, and cover index. That study presents the influences of fabric surface weight's parameter and the number of fabric sheet on the mechanical strengths of polymer composite based on phenol-formaldehyde reinforced PET's woven fabric. The experiments show that when surface weight of reinforced fabric increases, polymer composite's mechanical strengths have an upward tendency, tensile strength increases about 10 percent to 12 percent, compression and impact strength increases about 7 percent to 9 percent. In the condition of constant fabric mass, polymer composite used fabric of lower surface weight has a tensile strength increasing from 7.3 percent to 17.58 percent.