The invention relates to a carbon fiber reinforced polyester composite material and a preparation method thereof. The preparation method comprises the following steps: performing heat preservation oncarbon fiber coated with a thermosetting resin sizing agent at 250-350 DEG C for 0.5-15 minutes, then adding low-temperature heat-treated carbon fiber from a fiber feeding hole of a twin-screw extruder, adding a mixture of thermoplastic polyester, an antioxidant and a lubricant from a twin-screw extruder hopper, and extruding to obtain the carbon fiber reinforced polyester composite material withtensile strength of 160-220 MPa and bending strength of 240-290 MPa, wherein the mass ratio of the carbon fiber coated with the thermosetting resin sizing agent to thermoplastic polyester to the antioxidant to the lubricant is (20-40):(60-80):(0.1-0.3):(0.1-0.5). The preparation method has low heat treatment temperature and low energy consumption, the surface of the carbon fiber after treatment isrich in carboxyl groups which can react with thermoplastic polyester, which is beneficial to chemical bonding with thermoplastic polyester, and thus the carbon fiber reinforced polyester composite material has a great application prospect.