This book takes a gender perspective to conduct an in-depth, systematic analysis of the causes of the long-term high sex ratio at birth. It proposes the conception of social-mechanism concentrated in gender relations, its basic characteristics, and establishes the theoretical framework of gender mechanisms on high sex ratio at birth. It analyzes the process and the interactive relation of gender mechanism from the macro, meso and micro levels. It discusses the formation mechanism of the high sex ratio at birth, and proposes strategic choices and countermeasures in managing the high sex ratio at birth.