A resonant transformer includes a bobbin, a primary winding coil, plural secondary winding coils, and a magnetic core assembly. The bobbin includes a main body and a channel running through the main body. The main body includes a first winding section and plural single-trough second winding sections. Plural pins are arranged at the first winding section. The single-trough second winding sections are arranged at bilateral sides of the first winding section. The primary winding coil is wound around the first winding section of the bobbin and connected with the pins. The secondary winding coils are wound around respective single-trough second winding sections of the bobbin. The magnetic core assembly is partially embedded into the channel of the bobbin.