An electrophoretic display medium and preparing method thereof are provided. The electrophoretic display medium comprises: negatively or positively charged pigment particles; neutral pigment particles with colors different from those of the charged pigment particles; and low polar and/or non-polar dispersing solvent. The method of preparing the electrophoretic display medium comprises: synthesizing neutral pigment particles; synthesizing charged pigment particles; and preparing electrophoretic display medium. The method of synthesizing the neutral pigment particles in the electrophoretic display medium comprises: mixing together pigment particles, macromonomers, coupling agents and chain initiators for polymeric reaction in the solvent, and reacting in a temperature range of 30-120 degree centigrade for 4-48 hours. The method is applied to many kinds of inorganic oxides, inorganic salts and complex inorganic salt pigments. The present invention fundamentally avoids agglomeration caused by attraction of positively and negatively charged electrophoretic particles, therefore the display performance is greatly enhanced Besides, the steps of synthesizing particles are simple and the preparing procedure of the electrophoretic medium is simplified, and the whole process is simple and high efficient.