In order to meet the requirements of lightweight structural materials in extreme space environment，the T300，T700，and M40 carbon fiber-reinforced magnesium matrix composites （C_f/Mg） are fabricated by the pressure infiltration method.The effects of carbon fiber on the interfacial microstructures and mechanical properties of the C_f/Mg composites are investigated.The results show that there is a serious interfacial reaction product Al₄C₃ in both the T300/AZ91D and T700/AZ91D composites，which makes the composites brittle fracture under the low stress.However，the amount and size of Al₄C₃ are reduced significantly at the interfaces in the M40/AZ91D composites，which implies a moderate interfacial bonding strength.Therefore，the M40/AZ91D composite can fully exert its load transfer effect，and ultimately exhibits a high bending strength of 1 100 MPa.