The invention discloses an underwater instrument loading mechanism for fixed-point anti-offset aquatic weeds tangle-free, which structurally comprises an underwater instrument, a fixed-point positioning device and a driving device, wherein a magnetic fixer is pushed by a telescopic rod to move downwards to be tightly attached to an artificial fish reef, steel bars in the artificial fish reef are suctioned by electrifying a magnet through a lead wire to play a fixing effect, a contact plate is opened by water body because of water body when the magnetic fixer moves downwards, the water body influence disappears when the magnetic fixer is attached to the artificial fish reef, a restoring force is provided to drive the contact plate to be attached to the artificial fish reef and improve the fixing effect according to a return spring provided inside a rotation shaft, a centrifugal force is formed through the rotation of a transmission shaft, so that a cutting blade tip will move outwards to extend through a through hole to cut aquatic weeds and avoid entangling with the transmission shaft, blades rotate to form a centrifugal force making a slider to slide outward, the cutting blade tipis pushed to move in the fixed-point positioning device direction, so that aquatic weeds are prevented from being entangled on blades.