The invention discloses a preparation method of a rock sample for measuring the contact angle. The preparation method comprises the following steps of: (1) washing in oil and salt and drying; (2) preparing rock powder; (3) preparing an adhesion promoter; (4) preparing mixture; (5) filling into a mold; (6) pressurizing; (7) carrying out vacuum drying; (8) grinding and polishing; (9) wiping the endsurface. The preparation method disclosed by the invention has the beneficial effects that raw oil and salt remained in natural rock blocks are removed, and by the steps of crushing rock blocks, gluing, pressing, drying, grinding, polishing and wiping the end surface, the smooth surface of the prepared rock sample is realized and the accuracy and the repeatability of measurement of the contact angle are realized; the problems that due to unsmooth surface of the rock sample prepared by directly grinding and polishing a natural rock core, another two phases of fluid in the measurement process ofthe contact angle is contacted with the surface of natural rock core and rock sample and then enters microcracks or pores from the surface of the rock sample to cause inaccurate measurement of the contact angle, poor repeatability and failure in accurate measurement of data are overcome.