Background Mitochondrial respiratory chain is the major site to produce reactive oxygen species (ROS) when myocardium suffers from ischemia/reperfusion injury. As a main component of mitochondrial respiratory chain, complex Ⅲ completes electron transfer and oxidative phosphorylation with other complexes. As recent researches show, complex Ⅲ has taken an important role in cardial protection when preconditioning. Objective The review, based on the summary of the recent-year studies and researches, elaborates myocardial protection of complex Ⅲ and its mechanism in preconditioning. Content Complex Ⅲ is the major site to produce ROS in preconditioning. Such mechanisms as raising the mitochondrial membrane potential（mΔΨ） and changing the activity of complex III, etc, can mediate complex III to produce the ROS cardioprotection signaling molecule in preconditioning, thus protecting myocardium. Trend Explorations in the future researches will be on the mechanism of the regulation of the complex III to produce the ROS signal in preconditioning, and meanwhile strengthening the clinical application of complex III to produce ROS for the myocardial protection in preconditioning, which will provide strong method to clinical myocardial protection.