The invention relates to a flexible shaft fine adjustment self-lock device, which comprises a flexible shaft part, an adjustment part and a fixed part and the like, wherein a fixed portion of the adjustment portion substantially forms into a spiral groove through a spring which is engaged with a threaded pipe, an active portion of the adjustment part is formed through a steel pipe which is sleeved outside a steel bar, a round hole is arranged on the pipe wall of the steel pipe, a pit is arranged on the radial direction of the steel bar, the steel pipe is fixedly connected with a guy puller, which is equipped with a plane end and a smooth spherical end, a pressure spring is preloaded and arranged between the plane ends of the steel bar and the guy puller, and a pre-tightening force is keptthrough a spherical steel ball which is clipped between the round hole and the pit. The portion of the steel ball, which is exposed outside the round hole is jacked into the spiral groove which is formed through the spring which is engaged with the threaded pipe, and the spherical end of the guy puller is actively connected with a cupped guy joint which corresponds to a smooth spherical surface. The flexible shaft fine adjustment self-lock device has the main advantages that the position of the guy is capable of being accurately adjusted, the position of the guy is also capable of being adjusted in wider band, and a certain position of the guy is capable of being kept not changing in a long time.