The invention belonging to the technical field of lithium ion cells, and particularly relates to a method for improving hardness of a lithium ion cell by rapid formation. In the method, by adjusting the pre-baking time and temperature and the formation temperature of an electric core as well as the surface pressure on an electric core main body, the purpose of reducing the electric core polarization is achieved, high-current rapid formation is further realized, and finally the formation stopping potential is adjusted, so as to prepare the lithium ion cell with higher hardness. As compared with the prior art, the method has the following advantages: the high-temperature cramping and baking reshaping after formation is cancelled, so that the prepared electric core is higher in capacity; the electric core bears constant (or variable) pressure during the charge and discharge processes, thus the polarization in the charge and discharge processes is lower, and the capacity consistency of the prepared electric core is better; and because different temperatures and an SOC (state of charge) stopping manner are adopted for formation, the prepared electric core not only has excellent performance, but also has higher hardness.