The objective of the study was to investigate the feasibility of CUBE-SITR MRI and high-frequency ultrasound for the structural imaging of the brachial plexus to exclude neoplastic brachial plexopathy or structural variation and measure the lengths of anterior and posterior divisions of the C7 nerve, providing guidelines for surgeons before contralateral cervical 7 nerve transfer. A total of 30 patients with CNS and 20 with brachial plexus injury were enrolled in this retrospective study. All patients underwent brachial plexus CUBE-STIR MRI and high-frequency ultrasound, and the lengths of the anterior and posterior divisions of C7 nerve were measured before surgery. Precise length of anterior and posterior divisions of contralateral C7 nerve was measured during surgery. MRI-measured lengths of anterior and posterior divisions of C7 nerves were positively correlated with that measured during surgery (anterior division, r = 0.94, p < .01; posterior division, r = 0.92, p < .01). High agreement was found between MRI-measured and intra-surgery measured length of anterior and posterior divisions of C7 nerve by BLAD-ALTMAN analysis. Ultrasonography could feasibly image supraclavicular C7 nerve and recognize small variant branches derived from middle trunk of C7 nerve root, which could be dissected intra-operatively and confirmed by electromyography during the procedure of contralateral C7 nerve transfer. CUBE-STIR MRI had advantages for the imaging of the brachial plexus and measurement of the length of root-trunk-anterior/posterior divisions of C7 nerve. The clinical role of ultrasonography may be a simple way of evaluating general condition of C7 nerve and provide guidelines for contralateral C7 nerve transfer surgery.