The invention discloses a preparation method of an in-situ electrified transmission electron microscope section sample of heterojunction film; the preparation method comprises the steps of I, removing impurities on the surface of the heterojunction film sample; II, setting a layer of metal conductive film on the upper end face of the sample; III, attaching a copper sheet to the metal conductive film; IV, cutting the sample into a flaky sample; V, grinding to thin the flaky sample; VI, thinning the sample with an ionic thinner to obtain an arc recess; VII, transferring the sample to an in-situ test chip; VIII, using a focused ion beam instrument to weld a film layer interface and copper sheet, under electrical property test, of the sample respectively to an electrical property test electrode and power-on electrode of the in-situ test chip, and subjecting the copper sheet and metal conductive film to Pt layer welding; IX, cutting the sample to obtain a gap for breaking the metal conductive film. It is possible for the in-situ test chip to perform electrical property testing on the section sample of the heterojunction film, and operating is facilitated.