Objective: To simulate the tumor microenvironment though the 3D microtumor model which was constructed using droplet microfluidics.To explore its feasibility as a model for in vitro breast cancer research through3D microtumour fabrication,characterisation and sensitivity testing to chemotherapeutic drugs. Methods: Breast cancer cells were encapsulated with hydrogel shells in collagen-rich microencapsulated cores to obtain breast cancer microtumours in vitro;breast cancer microtumours were co-cultured with 3D microencapsulated endothelial cells by Transwell system.The structure and growth characteristics of the microtumours were directly observed by microscopy;the CCK-8 assay was used to detect the proliferation of the cells under different culture models and the drug sensitivity to doxorubicin;flow cytometry was used to compare the differences in apoptosis during the proliferation process;and the differences in the migratory and invasive abilities of the cells were assessed by scratch assay and Transwell assay;the expression of epithelial-mesenchymal transition-related proteins was detected by Western blot. Results: Breast cancer cells grew well in hydrogel nucleus-shell microcapsules;cell proliferation assays showed that 3D culture and 3D co-culture cells proliferated at a significantly lower rate than 2D culture;3D culture and 3D co-culture cells had enhanced migration and invasion ability and showed higher expression of EMT-related proteins compared to 2D culture;3D culture and 3D co-culture cells were significantly less sensitive to chemotherapeutic drugs compared to 2D culture.The sensitivity of 3D and 3D co-cultured cells to chemotherapeutic drugs was significantly reduced compared to 2D culture. Conclusion 3D cultures show similar morphology and biology to in vivo tumours and are more resistant to chemotherapeutic agents.