The invention provides a preparation method of a TEM sample. The preparation method comprises the following steps of 1, preparing a sample needing to be detected, wherein the sample is provided with a pattern needing to be detected, 2, cutting the sample to obtain a sample wafer, wherein the sample wafer comprises the pattern needing to be detected, 3, thinning the sample wafer from two opposite cut surfaces, and pasting a fixing ring on one of the thinned cut surfaces, 4, clamping the fixing ring, and through a Ga ion beam, bombarding areas which belong to one sample wafer surface provided with the pattern needing to be detected and are located at two sides of the pattern needing to be detected, so that the two sides of the pattern needing to be detected form pits, 5, clamping the fixing ring, and bombarding the thinned cut surfaces by an Ar ion beam, and 6, sequentially thinning an area comprising the pattern needing to be detected. The preparation method provided by the invention improves efficiency and reduces a cost.