The invention discloses a method for preparing a heat-conducting strip for a transformer. The method is characterized by comprising the following steps: S1, drying raw materials; S2, preliminarily mixing base materials to prepare a material A; S3, preliminarily mixing auxiliary materials to prepare a material B; and S4, performing twin-screw extrusion to form a heat-conducting strip, adding the material A and a mixture of an antioxidant, a light stabilizer and a flame retardant into a main feeding hopper of a twin-screw extruder, feeding the material B into a side feeding hopper, raising the temperature of a screw feeding section to (250+/-10) DEG C, raising the temperature of a melting section to (280+/-15) DEG C, raising the temperature of a homogenizing section to (260+/-10) DEG C, andblending, thereby obtaining the heat-conducting strip. According to the method disclosed by the invention, the material A is guided from the main feeding hopper to be reacted, polyphenylene sulfide and polyformaldehyde are promoted to achieve excellent heterogeneous nucleation characteristics by utilizing carbon nano tubes, the crystallization temperature of the polymer is increased, and the crystallization rate is increased. Moreover, the material is added from the side feeding hopper, polymer crystallization is induced to be performed along a direction of carbon fibers, and finally a heat-conducting net is formed to improve the heat-conducting effect of the material.