The invention discloses a method for preparing an in-situ tensile sample for a transmission electron microscope. The method comprises the following steps: selecting an area which meets low-index zone axis incidence, performing electrochemical polishing on a sample till the thickness of the sample meets the requirement of the experiment and keeping the surface of the sample flat, bright and clean; measuring the orientation of crystal particles by using a backscattered electron diffraction technique of a scanning electron microscope, selecting crystal particles which just meet a low-index zone axis, and marking the selected crystal particles; taking the selected crystal particles as an area which meets low-index zone axis incidence; and preforming a crack inside each selected crystal particle by using a focused ion beam machining technique, and in in-situ tension, preferably deforming the sample at the crack. The method has the advantages that the area which meets the low-index zone axis incidence can be easily found through the transmission electron microscope, and the purpose of dynamically observing high-resolution images of an object area in real time is achieved.