The yields and uniformities of Mn in high Mn-content (Mn≥10wt%) Mg-Mn master alloys have been studied in this paper. Pure Mn powder and Mg ingot were used to be raw materials and put into graphite pot. The master alloys were prepared by stirring cast in an induction furnace with Ar protection atmosphere at the operating power of 10KW. Master alloy melts were cooled in three different conditions, which were cooling in air with graphite pot, cooling in water with graphite pot and cooling in copper mould. The contents and distribution of Mn in master alloys were tested by GB\T 1506-2002. The results shown that the yields of Mn were improved with the increase of Mn particle size and the better uniformity was obtained by faster cooling speed of master alloy melt and smaller particle size of Mn powder, which were agree with the calculated results.