The present invention relates to a method for preparing propylene by disproportionation of ethylene and a long carbon chain olefin. According to the method, ethylene and a long carbon chain olefin are adopted as raw materials, and the ethylene and the long carbon chain olefin contact a transition metal oxide-containing catalyst and/or an alkaline earth metal oxide to carry out a disproportionation reaction to generate the propylene. With the technical scheme of the present invention, the olefin disproportionation reaction is adopted to convert the long carbon chain internal olefin into the high added value propylene and other basic organic chemical engineering raw materials so as to solve the reutilization problem of the long carbon chain internal olefin generated during the olefin oligomerization process, paraffin cracking process and other processes. The method of the present invention has advantages of high long carbon chain olefin conversion rate, high propylene yield, and the like, wherein the long carbon chain olefin conversion rate can be more than 90%, and the propylene selectivity can be more than 50%.