The invention relates to a method using a membrane separation technology to prepare hematoxylin powder dyes, comprising the following six steps: (1) adding water with the weight of 20-30 times in a crushed hematoxylin core material, and heating to 80-100 DEG C for extracting for 1-1.5 h and 2-3 times; (2) adopting a screen with 120-200 meshes for rough filtration; (3) filter paper sucking filtration; (4) adopting a polyvinylidene fluoride (PVDF) microfiltration membrane with a pore size of 0.1-0.4mum for removing impurities and bacterium; (5) adopting a hydrophobic polysulfone ultrafiltration membrane with intercepted molecular weight of 1000-5000 for concentrating extract liquid, concentrating to the solid content of retain liquid, namely pigment concentration liquid of 5-10%, and recycling permeation liquid with low-content hematoxylin power to extract hematoxylin pigment; (6) and spraying and drying to prepare the high-purity hematoxylin powder dyes. The method can reduce energy and water consumption in the preparation process of the hematoxylin dyes, and reduces the preparation cost and the dye impurity rate. The hematoxylin dyes can be used for developing green-feature textiles and can also be used for preparing hair dyes.