The invention relates to a method for treating leather by using tannery wastewater and a method for producing the leather. On one hand, the invention relates to the method for treating the leather by using the tannery wastewater. The method comprises the following steps of: (a) obtaining a near-infrared spectrum of the tannery wastewater generated by a tanning process by using a near infrared spectrum inductive probe; (b) determining or reading the concentrations of components in the tannery wastewater by the obtained near-infrared spectrum through a pre-established near-infrared spectrum data model; (c) supplementing raw materials into the tannery wastewater until the concentration required by the tanning process is reached according to the concentrations of the components in the tannery wastewater and obtaining the prepared tannery wastewater; and (d) treating the leather by using the prepared tannery wastewater and carrying out the tanning process, wherein the near-infrared spectrum data model comprises a corresponding relation between the near-infrared spectrum and the concentrations of the components. The method disclosed by the invention can be used for realizing recycling of the tannery wastewater and is an environment-friendly method for treating the leather.