Disclosed herein is a joint structure of a telescopic cylinder, the joint structure including a telescopic unit, an extension unit and a first fixing unit, wherein the telescopic unit includes a first main body, a first combined structure and at least one first fixing structure; the extension unit includes a second main body, a second combined structure and at least one second fixing structure; the first combined structure is screwed to the second combined structure; and the first fixing unit includes at least one first fixing body, and the first fixing body is simultaneously arranged in the first fixing structure and the second fixing structure and interferes with the first main body and the second main body so as to prevent the first combined structure and the second combined structure from spiral movement.