A medical hydrogel composition, a medical hydrogel, a preparation method therefore and an application thereof, and a medical hydrogel kit. The medical hydrogel composition comprises a first component and a second component; the first component comprises polylysine and polyethylene imine; the second component comprises one or more of 4-arm-polyethylene glycol-succinimidyl glutarate, 4-arm-polyethylene glycol-succinimidyl succinate, and 4-arm-polyethylene glycol-succinimidyl carbonate; the degree of polymerization of the polylysine is 20 or more. The medical hydrogel is formed by reacting the first component with the second component of the medical hydrogel composition. The medical hydrogel kit comprises the medical hydrogel composition and a buffer solution used for dissolving the components of the medical hydrogel composition. The medical hydrogel has a degree of swelling of −10%-50%, and can be applied in narrow parts where cranial, spinal, and peripheral nerves are densely distributed.