Objective To investigate the effect of spine disease on pelvic sagittal alignment and hip biomechanics in total hip arthroplasty (THA) patients. Methods The clinical data of 120 THA patients who had normal lumbar spine (control group) and 40 THA patients who had lumbar disease (lumbar disease group) between January 2013 and September 2015 in Shenzhen Longhua District People′s Hospital were analyzed. Radiographical parameters, like lumbar lordosis (LL), pelvic incidence(PI), pelvic tilt (PT) and sacralslope (SS) were collected and compared. Normal and pathological musculoskeletal simulation model was established based on standing and sitting X-ray pelvic alignment. Hip contact force, moment and muscle forces in standing posture and sitting to standing posture were calculated. Results The value of LL in lumbar disease group was shorter than that in control group:(34.23 ± 12.81)°vs. (47.26 ± 14.67)°, P＜0.05. Butthe value of PI in two groups had no significant difference (P>0.05). The value of PT and SS in two groups had significant differences: (17.51 ± 2.31)°vs. (8.31 ± 1.34)°,(27.61 ± 1.72)°vs. (38.01 ± 1.92)°, P＜0.05. At standing position and sitting moment position, the joint force and moment value between disease model and control model had significant differences (P＜0.05), and the differences were mainly in sagittal and vertical axis (P＜0.05). At standing position and the moment of sitting up, the extorsion muscle activation was at lower level and had no significant difference (P＞0.05). Conclusions Pelvic sagittal alignment pathology could change hip biomechanical situation, making threats to hip stability.