Abstract: Poly(methyl-benzene diethynylbenzene) silane (PSA) was used to modify dicyclopentadiene dioxide to give R-122/PSA, which was then fabricated into fiber reinforced composites. The curing mechanism and heat resistance of R-122/PSA were investigated by FT-IR、DSC and TGA. The mechanical strength, dielectric and water resistance properties of the fiber reinforced composite were studied. Results showed that the quality retention of R-122/PSA(mPSA/mR-122=0.2) was 30% higher than R-122 at 800 °C in nitrogen. The flexural strength of the composites was 735 MPa at room temperature and reached the maximum of 418.4 MPa at 220 °C. The water absorbing ratio of the composites in water for 96 h was up to 0.65%. R-122 modified with PSA can keep good mechanical properties and excellent heat resistance.