The invention relates to a method for preparing a coated flux tablet for XRF cobalt internal standard analysis. The method comprises the following steps: preparing lithium tetraborate and polyvinyl alcohol according to a mass ratio of 100:(2-3), uniformly mixing the lithium tetraborate with polyvinyl alcohol, and blending the obtained mixture with water to obtain a plastic material; weighing 1.10g of the plastic material, and pressing the plastic material to form a concave arc-shaped sheet in order to produce a crucible; preparing Co2O3 and Li2B4O7 according to a mass ratio of 0.11:1, and uniformly mixing the Co2O3 with Li2B4O7 to obtain a mixed powder II; and adding 0.9997-1.0003 g of the mixed powder II into the crucible, taking 1.00 g of the plastic material, uniformly covering the mixed powder II in the crucible with the plastic material, compacting the plastic material and the mixed powder II to form a blank, and drying and coating the blank to produce cobalt-containing coated flux tablets; and drawing 10 to N1/3 cobalt-containing coated flux tablets from N cobalt-containing coated flux tablets, detecting the Co2O3 content, and evaluating a preparation error to obtain the coated flux tablet for XRF cobalt internal standard analysis. The method has the advantages of high addition amount precision of an internal standard substance, evaluation of the error of the addition amount of the internal standard substance, high analysis efficiency, no transfer loss of the internal standard substance, and realization of addition of an oxidant.