The invention relates to a method for preparing a glass piece for cobalt internal standard XRF analysis based on a demould aid. The method is characterized in that: 0.1 g of cobalt trioxide, 6 to 7 gof lithium tetraborate and 0.1 g of a demould aid are mixed to obtain lithium tetraborate containing cobalt and the demould aid, which is referred to as a mixture I. 1 g of lithium carbonate, 0.15 to0.2 g of a demould aid, 0.05 to 0.08 g of iodide and 0.5 g of a sample are mixed to obtain lithium carbonate containing iodine and the demould aid, which is referred to as a mixture II. 5-6 g of the mixture I is placed in a platinum crucible, then the mixture II is placed, and covered with the remaining mixture I. the platinum crucible containing the mixture I and the mixture II is placed in a high temperature furnace, pre-oxidized at 680-720 DEG C, taken out, transferred to another high-temperature furnace, melted at 980-1050 DEG C, taken out, naturally cooled, peeled off, demolded, to obtainthe glass piece for the cobalt internal standard XRF analysis based on the demould aid. According to the invention, the method has the advantages of environmental friendliness, low cost and short cycle. And the manufactured product has high analysis accuracy.