The invention provides a 20 CrMnTi-based self-lubricating material taking spherical-structure Ag-Mg as a solid lubricant and a preparation method thereof. The method comprises the following steps of selecting Ag powder and Mg powder, adding the Ag powder and the Mg powder into an aqueous solution, drying, fusing and condensing treatment to obtain the spherical Ag-Mg solid lubricant; taking Fe powder, Cr powder, Mn powder, Ti powder, Si powder and the Ag-Mg solid lubricant with the total mass of 10-20 wt.% to obtain sintering matched materials through mixing treatment; and treating the sintering matched materials through a discharge plasma technology. According to the method, the spherical solid lubricant is in-situ composited in a 20 CrMnTi base body, so that the friction coefficient is small, and the wear rate is low. The self-lubricating material and the preparation method are favorable for further promoting the application of 20 CrMnTi-based gear material in the fields of aviation,spaceflight, metallurgy and the like, so that the lubrication of mechanical parts in extreme environments is met, and the service life and the use precision of the mechanical parts are improved.