Objective To study the influence of pre-operative disease course on the operation and post-operation quality of life of adolescents with idiopathic scoliosis (AIS). Methods A total of 110 AIS patients who were treated with classic posterior correction, pedicle internal fixation were divided into two groups according to their disease courses (n=55): short course group with a pre-operation course <2 years(S group), long course group with a pre-operation course ≥2 years(L group). The gender, Lenke type, and major curve Cobb angle were matchable between the two groups. Various radiographic measurements and indices like fusion level, intraoperative blood loss and scores of SRS-22 scale were compared between the two groups before operation, immediately, and 2 years after operation. Results The pre-operative Cobb angles of the major curve were similar between the two groups, but the flexibility of the major curve averaged (55.7±18.77)% in the S group and (48.1±18.24)% in the L group (P=0.034). Pre-operative Cobb angles of the minor curve were larger in L group than those in S group (\[30.1±12.10\]° in the S group and \[34.8±10.85\]° in the L group, P=0.035). The post-operative radiographic measurements and the blood loss/infusion were similar between the two groups. The number of fused vertebrae in the L group was significantly more than that in the S group (P=0.027). The parameters in the SRS-22 scale, including function/activity, pain, self-image/appearance, and mental health were similar between the two groups during follow-up. And the L group had a significantly lower satisfaction rate of treatment compared with the S group (\[4.0±0.70\] vs \[3.7±0.78\], P=0.037). Conclusion The flexibility of the curve in AIS decreases with the increase of disease course, and the disease course might be a risk factor for the scoliosis progression of the minor side. Patients with a disease course ≥2 years have more fused vertebrae than those with a disease course <2 years. The length of pre-operative disease course has influence on the quality of life of AIS patients after operation.