The invention discloses a PET aluminum-plated base membrane and a preparation method thereof. The PET aluminum-plated base membrane comprises a core layer in the middle and surface layers arranged on the two surfaces of the core layer. The surface layers and the core layer are integrally formed through co-extrusion and two-way stretching. The core layer is a PET layer, and the surface layers are PET layers mixed with anti-adhesion agents. The preparation method includes the steps of polyester synthesis, mixing, co-extrusion, sheet casting through a die, longitudinal stretching, transverse stretching, traction and trimming, corona treatment, coiling, cutting and obtaining of a finished product. The PET aluminum-plated base membrane can be prepared through the preparation method, and has excellent light transmittance and surface tension. The light transmittance can reach 89%, the glossiness is 130, the surface tension can reach 58 dyne, and the light transmittance, the glossiness and the surface tension can keep for a long time and do not weaken. Aluminum-plated membranes meeting different packaging requirements can be produced, and the produced aluminum-plated membranes are uniform and high in aluminum layer bonding force.