The invention relates to a synthesis method of a ternary molybdenum nitride. The synthesis method is characterized in that a ternary molybdenum nitride (TnMo3N) nano material is prepared under a mild condition by adopting one-step chemical reaction; the synthesis method comprises the following steps: accommodating metal molybdenum powder, a metal T source compound and sodium azide in a reaction kettle, and heating to 600 to 800 DEG C, wherein the reaction time is 5 to 40 hours; cooling; washing a product; filtering, separating and drying, thus obtaining the ternary molybdenum nitride (TnMo3N) nano material, wherein the yield is up to 90 percent or more.