The invention discloses a composite insulator which comprises the components of a porcelain core (1), a glass fiber layer (2) which is arranged outside the porcelain core (1), an adhesive layer (3) which is arranged on the glass fiber layer (2), and a silicone rubber umbrella sleeve (4) which is arranged outside the adhesive layer (3), wherein the porcelain core (1) comprises an original segment and a glazed segment. The invention further provides a preparation method of the insulator. According to the composite insulator, the porcelain core is used as a main core rod and has higher rigidity, higher deformation resistance and higher aging resistance. Furthermore the surface of the porcelain core is provided with the un-glazed original segment, thereby improving surface activity so that the glass fibers can be wound and adhered more closely, and preventing defects such as aging and falling-off. Furthermore, by means of relatively surface activity and surface roughness of the glass fiber, adhesion between the glass fiber layer and the silicone rubber umbrella sleeve is firmer than adhesion between the porcelain core rod and the silicone rubber umbrella cover.