The invention discloses a method for preparing propylene through an ethylene/butylene disproportionation reaction. The method is characterized in that ethylene and 2-butylene contact with a carbene catalyst solution containing metallic ruthenium or osmium to generate propylene; and especially, ethylene and 2-butylene contact with the carbene catalyst solution containing metallic ruthenium or osmium under conditions comprising that the temperature is 0-50DEG C and the pressure is 0.1-10MPa to generate propylene, wherein the molar ratio of ethylene to 2-butylene is 1:1-10:1. The method has the advantages of simple process, mild technological condition, high reaction conversion rate, high reaction selectivity, no need of the regeneration of the catalyst, and the like.