OBJECTIVE To study the rotary angle and image features, so as to help early diagnosis. METHODS Four adult cervical spine (C1-T1) specimens were used, including 2 males and 2 females,ranging in age from 28 to 40 years old. X-ray and CT examination were performed before the experiment. C2-C4 and C5-T1 were fixed respectively using self-made clamp. Unilateral locked facet of cervical spine was simulated under the violence of inflection and rotation, in which the muscle contraction was partially simulated, and at last the plain radiographs and CT of unilateral locked facet of cervical spine were analyzed. RESULTS In unilateral locked facet of cervical spine, the average rotary angle was 19.75 degrees, and average forward shift of vertebral was 3.68 mm. The intervertebral foramina below the injury plane were showed at 0 degrees,10 degrees, 180 degrees,190 degrees; the intervertebral foramina above the injury plane were showed at 150 degrees,160 degrees, 00 degrees, -10 degrees, and the facet was locked or in disorder at the injury plane. The intervertebral foramina at the anterior oblique position was bigger in interlocking side, but it was smaller in the opposite side. CT scan showed rotary spine, the naked facet sign; coronal plane reconstruction showed bilateral asymmetry; sagittal plane reconstruction obviously showed unilateral locked facet. CONCLUSIONS X-ray and CT both can independently diagnose unilateral locked facet of cervical spine. CT and three-dimensional reconstruction are more better than X-ray to diagnosing it.