To provide a crosslinkable ionic water soluble polymer powder which can be easily prepared at a low cost and with high performance, and its preparing method and its using method.

The crosslinkable ionic water soluble polymer powder can be prepared by polymerizing a high concentration aqueous solution composed of a monomer mixture comprising (A) a water soluble cationic vinyl monomer and (B) a water soluble polycation crosslinking agent to be represented by formula (1) as the essential components, and optionally one or more kinds to be selected from (C) a water soluble anionic vinyl monomer and (D) a water soluble nonionic monomer, evaporating the water content of the above aqueous solution by polymerization heat of the above polymerization to obtain a low water content polymerized product, and rendering the obtained product fine particles suitably through a drying step.