The invention relates to the field of the spaceflight ground simulated test, in particular to a butt-joint mechanism six-freedom-degree gravity balance following mechanism. The butt-joint mechanism six-freedom-degree gravity balance following mechanism comprises a balance crane connecting arm, a middle connecting arm, a gravity balance bearing arm, a U-shaped frame and a branch support assembly. The two ends of the middle connecting arm are rotationally connected with the balance crane connecting arm and the gravity balance bearing arm correspondingly. Two brake mechanisms are arranged on themiddle connecting arm. The balance crane connecting arm and the middle connecting arm are braked through the different brake mechanisms for rotation. An intelligent balance crane is arranged at the end portion of the balance crane connecting arm and connected with the upper end of the U-shaped frame through a steel wire rope. The lower end of the U-shaped frame is connected with the branch rod assembly in the butt joint mechanism. During test, one end of an aircraft simulation piece is connected with a butt joint mechanism, and the other end of the aircraft simulation piece is connected with the end, away from the middle connecting arm, of the gravity balance bearing arm. When the butt joint mechanism is subjected to the ground test, gravity balance floating control and six-freedom-degreerapid following can be achieved.