With the acceleration of industrialization, urbanization, as well as the reform and opening-up, the amount of migrant workers is increasing sharply. However, the specialty of criminal cases is ignored, rights of migrant farmers and legal aids for them are neglected, making them commit crimes for lack of basic knowledge of laws and failing to be treated with fairness. The aim of enjoying human rights is a failure. Based on the legal aids for migrant workers, the paper discusses how to protect legal rights of migrant workers in criminal cases and make them enjoy fairness of laws, making laws play a true part in criminal cases and fulfill the aim of human rights protection.