Heavy metal contamination presents serious threats to living organisms. Functional genes related to cadmium (Cd) hypertolerance or hyperaccumulation must be explored to enhance phytoremediation. Sedum alfredii Hance is a Zn/Cd cohyperaccumulator exhibiting abundant genes associated with Cd hypertolerance. Here, we developed a method for screening genes related to Cd tolerance by expressing a cDNA-library for S. alfredii Hance. Yeast functional complementation validated 42 of 48 full-length genes involved in Cd tolerance, and the majority of them were strongly induced in roots and exhibited diverse expression profiles across tissues. Coexpression network analysis suggested that 15 hub genes were connected with genes involved in metabolic process, response to stimuli, metal transporter and antioxidant activity. The functions of a novel SaCTP2 gene were validated by heterogeneous expression in Arabidopsis, responsible for retarding chlorophyll content decreases, maintaining membrane integrity, promoting reactive oxygen species (ROS) scavenger activities and reducing ROS levels. Our findings suggest a highly complex network of genes related to Cd hypertolerance in S. alfredii Hance, accomplished via the antioxidant system, defense gene induction and the calcium signaling pathway. The proposed cDNA-library method is an effective approach for mining candidate genes associated with Cd hypertolerance to develop gene-modified plants for use in phytoremediation.