A locking and unlocking nut structure contains a body including a through hole and a semi-circular recess, and the semi-circular recess having a starting segment and a stopping segment, the body further including a diameter-decreased screw section; a slidable block including a C-shaped cutout, and the C-shaped cutout including an engaging hook extending outward from a lower end thereof, the slidable block including first threads, while the slidable block is fixed on the starting segment, a distance from the first threads to an inner wall of the through hole is larger than an outer diameter of the screw rod (tube); while the slidable block is fixed on the stopping segment, a distance from the first threads to the diameter-decreased screw section is equal to the outer diameter of the screw rod (tube); the screw rod (tube) including second threads to match with the diameter-decreased screw section and the first threads.