A nut and support element assembly structure includes: a nut having a screw hole, an end side, and a lateral side; a support element having a bottom resting portion, two end side abutting portions disposed at the end sides of the nut, respectively, and two lateral side clamping portions connected to the end side abutting portions to clamp the nut from the lateral sides. A nut and support element assembly structure includes: a nut having a screw hole, an end side, and a lateral side; a support element having a bottom resting portion, two end side abutting portions disposed at the end sides of the nut, respectively, and two lateral side clamping portions connected to the bottom resting portion to clamp the nut from the lateral sides. A screwing-fixing assembly for use with the nut and support element assembly structure is further provided.