The thermoplastic polyetethylene was used as the Matrix and PET fiber was used as the Reinforcement. The sample of board were from by mixing, blowing and hot pressing. The study on that blowing action, desity, changing size and stength by means of changing blowing agent, length and percentage of PET fiber. The results indicate that the best treatment condition is found to CAB 2.4 g, PET fiber 2.5 cm, 20%.