Using cyclopropyl methyl ketone as starting material and phosphorus pentachloride as chlorination reagent, cyclopropyl acetylene, the key intermediate of Efavirenz, was synthesized by chlorination followed by elimination. Aiming at the different eliminating reactivity between the dichloride and monochloride intermediates, the stepwise elimination reactions were carried out in the presence of triethylamine and potassium hydroxide, respectively. A one-way yield as high as 49% of cyclopropyl acetylene was obtained based on cyclopropyl methyl ketone. At the same time, the recycling process for triethylamine has been established, which further reduces the cost and has good prospects for industrialization.