The stability of grass carp hemoglobin (GCH) and its impact on lipid and protein oxidation under different pH conditions (pH 6.0, 6.5, 7.0, 7.5, and 8.0) were investigated. The results indicated that under acidic conditions (pH 6.0 and 6.5), the oxyhemoglobin (OxyHb) level decreased significantly, with the relative oxygenation rate reduced by 30% and 14% at 96 h, respectively. These values were significantly lower than those under neutral and alkaline conditions (at pH 7.0~8.0). Methemoglobin (MetHb) formation reached 4.92 μmol/L (6 μmol/L) and 4.3 μmol/L (6 μmol/L) at 72 h, which was significantly higher than that under neutral and alkaline conditions (P<0.05). The oxygen-binding capacity of GCH weakened under acidic conditions, leading to the autoxidation of MetHb. Under acidic conditions, the maximum POV values in the GCH group reached 16.1 μmol/kg and 16.2 μmol/kg, and the maximum TBARs values were 4.9 mg MAD/kg and 4.5 mg MAD/kg. These were significantly higher than those under neutral and alkaline conditions (P<0.05). Under acidic conditions, the total sulfhydryl contents in the GCH group were lower than those in alkaline conditions. Conversely, the carbonyl and dimerized tyrosine contents in the GCH group under acidic conditions were higher than those under alkaline conditions and the control group. These findings indicated that protein oxidation is accelerated by GCH under acidic conditions. The results suggest that the autoxidation of GCH to form MetHb under acidic conditions is the primary factor contributing to the rapid oxidation of lipids and proteins in fish, whereas hemoglobin-mediated lipid and protein oxidation is inhibited under alkaline conditions. Hence, it is suggested that increasing the pH of the fish mince processing environment could assist in improving the preservation and storage of fish products.