Abstract: The short glass fiber/epoxy resin (GF/EP) composites with 0.5wt% GF were fabricated through casting method. The properties of GF/EP composites length 1 mm, 3 mm and 5 mm were studied, respectively. The mechanical properties and thermal properties of GF/EP composite and the tensile strength of the fiber tow with surface treatment of polyimide (PI) were investigated. Polyimides with reactive phenolic hydroxyl groups (PI1) and without (PI2) were prepared. The results show that tensile strength and strand integrity of the GF are improved. The tensile strength of GF treated with PI1 is increased from 517 MPa to 1 032 MPa and PI2 is increased to 986 MPa. GF/EP composites have the best mechanical properties when 3 mm GF treated with PI1, and tensile strength, tensile modulus, flexural strength and fracture toughness of PI1-GF/EP composites are increased by 23.62%, 34.03%, 28.74% and 13.04% respectively. The mechanical properties of GF/EP composites with treatment of PI2 are slightly improved. The tensile strength, tensile modulus, flexural strength and fracture toughness are increased by 15.87%, 23.70%, 14.11% and 4.05%, respectively. The glass transition temperature of PI2-GF/EP composite is significantly improved by treating GF with PI.