The size of copper precipitates is the main factor affecting the antibacterial performance of antibacterial stainless steel. To study the mechanism of copper precipitate growth in ferritic stainless steel, the shape coefficient η and average specific interfacial energy of copper precipitate σ ¯ were calculated. The growth process of copper precipitate was observed by atomic probe tomography and transmission electron microscope. The results show that the shape coefficient of copper precipitate was 3.053, and the average specific interfacial energy was σ ¯ = 0.4832 - 0.1652 × 10 - 3 T . The increase in the aging time resulted in an increase in the size of copper precipitates and a decrease in the number density. In addition, with the increase in the aspect ratio, the shape of the precipitated phase changed from an initial spherical shape to ellipsoid shape and finally to a rod shape. The increase in the annealing time enhanced the antibacterial activity of the tested steel until almost 100% of the bacteria were killed. Thus, the antibacterial performance is closely related to the size and total surface area per unit area of the precipitate.