The invention particularly relates to a dark blue and white color material water-based dispersing agent for ink-jet printing and a preparation method and application mode thereof. The dispersing agent contains a flexible polysiloxane main chain. The main chain contains dopamine units and primary amino and further contains a polyether side chain with carboxyl. The dopamine units and the primary amino can achieve a stable matching effect firmly with manganese oxide color material particle surfaces, iron oxide color material particle surfaces and chrome oxide color material particle surfaces. The polysiloxane main chain can guarantee that molecules of the dispersing agent are attached to the color material particle surfaces as much as possible, and the surface tension of ceramic ink can be reduced. The polyether side chain with carboxyl can be dispersed in water, and under the alkalescence condition, carboxyl is subjected to ionization, a negative electricity layer is produced on the surfaces of color material particles, and reunion and sedimentation of color material particles are further restrained.