Disclosed is a cell sheet for tissue repair and bio-artificial tissue engineering. The cell sheet comprises treated stem cell embedded in its self-secreted extracellular matrix (ECM) and formed a cell sheet. The cell sheet is formed by isolating the stem cell, expanding the stem cell and treating the stem cell with biological factors or factors leading to the production of biological factors, to induce its differentiation, production of extracellular matrix and formation of a cell sheet in vitro. The cell sheet is used as a bioactive material or as an acellular material for the promotion of tissue repairs or used to form a bio-artificial organ for tissue replacement. The cell sheet of the present invention eliminates the need to use scaffolds for cell delivery. The cell sheet facilitates in vivo cell transplantation and provides some tensile mechanical strength for bearing early mechanical load during tissue repair.