Objective To investigate the jaw changes in class Ⅱ jaw′s malocclusion patients who were firstly treated with unexacted and exacted treatment in fix appliance in the accelerated stage of cervical vertebrae maturation by cephalometric analysis before and after treatment.Methods For 24 class Ⅱ Jaw′s malocclusion patients who were firstly treated with fixed appliance at the accelerated stage of cervical vertebrae maturation,their cephalometric films were taken before and after treatment.19 mandibular and dental items were measured and analysed.Statistics paired-sample and Independent samples t test were performed in SPSS 10.0.Results ①After treatment,subspinale,supramental and pogonion points became lower,length of mandibular body,ascending ramus,anterior facial height,posterior facial height and low facial height became longer,maxillary-mandibular skeletal relationship was more "normalized" and the angle of mandibular plane was almost the same in 24 subjects.② Only the changed magnititude of the lower incisor oblique angle had obviously statiscal difference between two groups.The nonexacted group was bigger than exacted group.Other variables didn′t have obviously stastistical difference.Conclusion The accelerated stage of cervical vertebrae maturation is the better time to start the fix treatment in class Ⅱ jaw′s malocclusion patients and there isn′t obvious difference in the improved effects of class Ⅱ′ jaw.