Traditional method: put a big bed sheet on the mattress, the center line of the big bed sheet is aligned with the center line of the bed, and spread out to the end of the bed respectively; Put the big sheets on the bed first: one hand holds up the corner of the mattress and the other hand extends across the center line of the bed. Tighten the big sheets and fold them under the bed. At a position about 30cm away from the bed, lift the edge of the big bed sheet upward to make the end of the big bed sheet form an equilateral triangle, and then put the two bottom corners under the bed respectively. Spread out the big sheets at the end of the bed in the same way, and tighten the middle edge of the big sheets with both hands and stuff them under the mattress. Turn to the reverse side, and spread the large sheet on the reverse side in the same way [1] 1.2.2 Improvement method: ① Fold the large sheet: face up and fold it horizontally twice: when it is folded in half for the first time, the edges are aligned; When folding in half for the second time, leave a loose edge of about 30CM, and then fold the two layers of loose edge of 30CM upwards to cover the horizontal center line of the large sheet, as shown in figure 1 (omitted), with the edges aligned. ② Operation method: stand at the end of the bed, facing the head of the bed, and put the big bed sheet at the end of the bed, with the loose edge of the big bed sheet at the upper end, with the transverse midline of the big bed sheet aligned with the edge of the mattress and the longitudinal midline aligned with the midline of the mattress. Spread it out to both sides, revealing two single-layer sheets folded 30CM, and turn down the upper layer.