Breast cancer is one of the most common epithelial tumors and can seriously endanger women's health. Studies have shown that carcinoma-associated fibroblasts (CAFs) possess myofibroblast features and play an important role in the growth and metastasis of breast cancer. Because of the lack of an applicable animal model, the exact role of CAFs in tumor metastasis is still unclear. In this research, a simple three-dimensional (3D) cryogel co-culture system was developed to evaluate the role of CAFs in breast cancer metastasis. It was found that CAFs could promote epithelial–mesenchymal transition of MDA-MB-231 cells (human breast cancer cells) in a 3D cryogel co-culture system in vitro. Then the co-culture human breast cancer system was used to construct a xenograft tumor mouse model in vivo. It was found that CAFs could promote deterioration and metastasis of MDA-MB-231 cells in a xenograft tumor mouse model in vivo.