The present invention relates to a method for preparing water soluble vinyl-sulfone polyurethane class high molecular reactive dye with a diazo coupling method. A polyurethane precursor is used as a high molecular skeleton, diazo salt is then prepared from hydroxyethyl sulfone sulfate class arylamine, the diazo salt finally has diazo coupling reaction with the polyurethane precursor, and the water soluble vinyl-sulfone polyurethane class high molecular reactive dye is prepared. The dye having good water solubility can react with materials containing hydroxy or amino groups under alkaline conditions to complete color fixation. The problems about dyeing fastness, etc are solved. The method has the advantages of simple synthesis thought, easy functionality control, high diazo coupling rate, etc. The dye can be used for dyeing materials containing cotton, hemp, silk, fur, leather, paper, etc, can be used in the spinning processing of spandex stock solution for preparing colored spandex, can be used as the coloring agent and the filler of plastics, rubber, paint and adhesives, and can be used as the coloring agent ingredient of digital jet printing ink.