The present invention relates to a preparation method of water-soluble pectin of shaddock albedo. The method comprises the following steps: bake drying or naturally drying shaddock albedo and cutting the shaddock albedo into chunks, immersing the shaddock albedo chunks into 95% ethanol for more than 12 h and drying; adopting a hot water extraction method to prepare the water-soluble pectin with a ratio of the shaddock albedo to water being 1: 10-1: 50 at a temperature of 60-100 DEG C, carrying out extraction for 1 to 3 times each lasting 1 to 5 h, and stirring constantly; filtering extraction liquid to obtain a supernatant; concentrating the supernatant to 1 / 8 to 1 / 10 of the original volume, carrying out alcohol precipitation for 12 h, centrifugating for 5 to 10 min at a speed of 3000 r/min to 4800 r/min, collecting the precipitation, drying the precipitation at a temperature of 40-55 DEG C, and then obtaining the water-soluble pectin. According to the present invention, the waste of shaddock peel is reused, resource utilization is improved; the preparation method has high extraction efficiency and no toxic and hazardous organic reagent, and the product is safe; the process is simple, and the application prospects are extensive.