The cryoprotective effect of degraded konjac glucomannan (KGM) on the grass carp myofibrillar was studied and five degradation methods including acid hydrolysis, enzymatic hydrolysis (dextranase, cellulase), γ-irradiation hydrolysis, and microwave assisted hydrolysis with hydrogen peroxide were used. The cryoprotective effects of KGM with different degradation products were compared and freezing points were also measured. The results showed that the degradation products of KGM had a cryoprotective effect on the grass carp myofibrillar during the frozen storage. When the amount of degraded KGM (enzymatic hydrolysis, γ-irradiation hydrolysis) was 0.5%, the cryoprotective effect was better than that of commercial cryoprotector. The degraded KGM could decrease the freezing point and enthalpy of water as a new cryoprotector.