The invention discloses a synthesis method and a purpose of a steroidal acetylene acid compound. The synthesis method comprises the following steps that in a non-protonic solvent, under the effects oflight illumination and oxygen gas, a compound 2 and a photosensitizer are subjected to the following reaction to obtain a compound 1. The synthesis method provided by the invention is a Furan photooxidation ring opening method. The method can be used as a steroidal degradation method; alkynyl and carboxyl bifunctional products can be conveniently generated, and can be used for synthesizing a steroidal compound of a relevant structure. The compound 2 and the compound 1 are shown in the description.