There is provided a method for preparing an analytical standard used for microbeam X-ray fluorescence analysis which includes: a mixing step in which an element is added to a base material, and the base material and the element are mixed by stirring to obtain a mixed solution; a deaeration step in which the mixed solution is deaerated; a freeze step in which the mixed solution is slowly frozen; and a cutting step in which a thin section is cut out from the frozen mixed solution. In order to surely remove bubbles from the mixed solution, the deaeration step may contain a stationary step in which the mixed solution is allowed to stand still at room temperature; or the stationary step includes a removal step in which gas contained in the mixed solution which is allowed to stand still is removed with a suction apparatus.