Aiming to explore the effect of lactic acid-LDH-NAD system on NADH regeneration and MetMb reduction ability of yak meat mitochondria in electron transport chain (ETC). The effects of lactate on mitochondrial membrane permeability, membrane potential and the role of Lactate-LDH system in NADH regeneration and MetMb reduction in vitro were investigated. Depending on the treatment, the mitochondrial membrane permeability and mitochondrial membrane potential were decreased in the lactate treatment group, and the oxygen consumption rate and MetMb reduction in the CaL+LDH+NAD system group were the highest in all the experimental groups (P＜0.05). In the presence of antimycin A, NADH produced by CaL-LDH-NAD treatment cannot perform oxygen consumption. When Mb was only incubated with mitochondria, the Mb redox state in the system hardly changed (P＞0.05), and NADH formed by LDH couldnot restore MetMb without reductase or electron carrier. The addition of the LDH inhibitor sodium sulphate treatment group reduced the reduction of MetMb by the CaL-LDH-NAD combination (P＜0.05), but at the same time, sodium oxalate did not completely inhibit the reduction of MetMb, except for the electron transport chain mediated. In addition to nonenzymatic reduction, NADH produced by the CaL-LDH-NAD system can also be used for enzymatic MetMb reduction in mitochondria. It was indicated that mitochondrial metabolism was related to flesh color, and the oxidation process of lactate was the cause of MetMb reduction. At the same time, the reduction equivalent of mitochondria can affect oxygen consumption, MetMb reduction, and Mb redox state and beef color stability.