One of the reasons for many social tragedies resulted from land expropriation in China is failure of the constitution to bring into play its due functions in standardizing land expropriation power of the government and protecting farmers’ rights. In the existing land expropriation system, government is not only a policy maker of land expropriation, but also a “referee” of dispute over land expropriation. Government’ land expropriation power and land-expropriated farmers’ rights become out of balance. As a result, some local governments do not attach importance to farmers’ rights, making land-expropriated farmers dissatisfied and consequently leading to some social tragedies unfavorable for harmony and stability. To fundamentally settle disputes over land expropriation and realize win-win of farmers’ right and state interest, it should bring into full play functions of the constitution through protecting farmers’ right to participate in land expropriation and establishing constitution evaluation mechanism.