The invention relates to a one-pot 5-HMF (5-hydroxymethylfurfural) preparation method based on an MTO (methyltrioxorhenium) composite catalyst. The method comprises steps as follows: an appropriate amount of MTO, a metal chlorine salt and an ionic liquid are taken and dissolved sufficiently at the temperature of 90-100 DEG C, the composite catalyst is prepared, an appropriate amount ofmicrocrystalline cellulose or lignocellulose is added, the mixture reacts for 10-60 min at the temperature of 110-150 DEG C, and the target product, namely, 5-HMF is obtained. 5-HMF is prepared with a one-step method through direct degradation of cellulose, the reaction process is simple, the yield of 5-HMF is higher, and the catalyst MTO is environment-friendly and free of environmental pollution.