The invention provides a method for preparing PUR (polyurethane reactive) hot melt adhesive from trimethylpyridine-phosphamide. A drying process is not required, the problems about environment pollution and poisoning due to existence of a solvent can be solved, the environmental protection requirement is met, a adhesion technology is simple and convenient, roller coating or spraying and other adhesive application methods can be adopted, the operability is better, two adhered bodies can be fixed in a short time, accordingly, an assembly part can be rapidly shifted to the next preparation procedure, and the work efficiency is improved; the hot melt adhesive has the advantages of heat resistance, cold resistance, water vapor resistance, chemical resistance and solvent resistance. Compared with original hot melt adhesive, the hot melt adhesive has the substantially improved properties and adhesion strength because of the crosslinking structure of the reactive hot melt adhesive.