The invention provides a preparation method of a high-concentration CO methanation catalyst. The preparation method comprises the following main steps: (1) preparing nickel nitrate hexahydrate, carrier component water soluble salt, first auxiliary water soluble salt, second auxiliary water soluble salt and a dispersing agent into an aqueous solution, so as to obtain mixed solution A; (2) mixing water soluble carbonate and bicarbonate to obtain an aqueous solution, i.e., mixed solution B; (3) slowly adding the mixed solution B into the continuously stirred mixed solution A, then heating to an aging temperature, and aging; and (4) transferring an aged sample into a hydrothermal reaction kettle, carrying out hydrothermal treatment; and finally washing, filtering, drying and roasting, so as to obtain the high-concentration CO methanation catalyst. The catalyst prepared by adopting the preparation method provided by the invention has the advantages of low initial activation temperature, anti-sintering property as well as good water resistance and thermal stability.