Abstract: Fiber mass fraction was one of the key factors that affect the preparation of high-performance fiber composites by vacuum assisted resin transfer molding (VARTM). This research studied the influence of bamboo fiber (BF) mass fraction on the epoxy resin (EP) impregnated fiber effect and the performance of BF/EP composites made by VARTM, which provided theoretical support for the practical application of bamboo fiber composites. The bamboo fiber bundles were made into bamboo fiber mat by wet layering, using the VARTM process to prepare the fiber mass fraction of 0wt%, 15wt%, 25wt%, 35wt% and 45wt% BF/EP composites. The resin-impregnated fiber effect, water absorption, mechanical properties, and heat resistance of BF/EP composites were characterized by ESEM, ultra-depth-of-field microscope, mechanical testing machine, TG and DMA. It is observed that the difficulty of EP injection and the water absorption rate of BF/EP composites gradually increases with increasing fiber mass fraction. The water absorption rate of the BF/EP composites increases significantly when the fiber mass fraction is 35wt% or more. The mechanical interlocking between BF is stronger in BF/EP composites with higher fiber mass fraction, which can effectively disperse the failure stress, leading to higher mechanical performance, compared with 15wt%, the flexural strength, flexural modulus, shear strength and impact toughness of 45wt% BF/EP composites are significantly improved by 84%, 64%, 103% and 101%, respectively. The pyrolysis rate of BF/EP composites with increasing fiber mass fraction increases when the temperature is lower than 380℃ and decreases when higher than 380℃, when the fiber mass fraction is more than 35wt%, the amorphous carbon obtained from the thermal decomposition of the BF can be used as a protective layer to reduce the penetration of volatile degradation products into the BF/EP composites and delay the pyrolysis reaction. When the fiber mass fraction is 45wt%, the dense bamboo fiber mat can limit the movement of the resin molecular segments, thereby improving the heat resistance of the BF/EP composites. The BF/EP composites prepared with fiber mass fraction at 45wt% can be used in the fields where the characteristics of high performance, low cost are required, such as indoor decoration.