Abstract: The deposition experiments were done on the mild steel by micro-plasma arc powder overlaying rapid prototyping technique with Fe313 alloy powder.The microstructures and morphologies were observed by metallographic microscope and SEM,the microhardness was tested by vickers.It was showed that the middle layer displayed insular M-A component structure,and the interface between layers was evident.The microstructure of Fe-based deposited layer was affected by the subsequent overlaying with annealing process,and the crystalline grain refined.The hardness distribution curve of the cylindraceous part was as U shape,the middle layer was soften because the drawing effect of subsequent layers.