The invention relates to the field of hydrogel preparation, in particular to injectable polymer hydrogel based on an acylhydrazone bond, a preparation method thereof and a polymer hydrogel injection.The injectable polymer hydrogel based on the acylhydrazone bond comprises the raw materials of a first component obtained by modifying a hydrazide-based polysaccharide polymer, and a second componentobtained by modifying aldehyde-based polyvinyl alcohol, terminal-hydroxyl-based polyethylene glycol, and/or polyethylene oxide-polypropylene oxide-polyethylene oxide. The adding mass ratio of the first component and the second component meets that the range of hydrazide-based substitution degree/aldehyde-based substitution degree is 20-80%, and the balance water solvent is added. Very high fluidity is achieved within a few minutes after prepolymers of the first component and the second component are well mixed, and the prepolymers can be immediately injected to a specific mould or position tobe formed; if the prepolymers of the first component and the second component are mixed and subjected to gelatination, the injectable property is still achieved; the first component and the second component both have very excellent structure compatibility; and the certain fluidity is shown after the first component and the second component are mixed.