Objective To evaluate the correlation of L4 / 5 multifidus fat infiltration with lumbar range of motion and quality of life in patients with degenerative spinal deformity. Methods:Including 30 DSD from 2018 to 2021.Measuring the Cobb angle,LL,TK and TK / LL after completing the full-length spinal tablet.35 healthy volunteers as a control group,The general conditions and history of underlying disease were collected for both populations,FI of L4 / 5MM was obtained by element spectroscopy(Single-voxel MR spectroscopy, SV-MRS).Using a joint anglometer to measure the lumbar anterior flexion,posterior extension,left and right lateral flexion direction ROM,The lower back pain was assessed before testing using the pain VAS,Participants' quality of life was assessed using the RDQ.By evaluating the difference between LROM,MMFI,and RDQ,the correlation of RDQ scores with MM FI,ROM,Cobb angle,LL,TK,and TK / LL,respectively.Results: The VAS score was higher in the DSD group than that in the control group (p<0.05);In terms of consistency,the DSD group has good forward flexion and posterior extension reliability,strong convex lateral flexion reliability and general concave lateral flexion reliability.The control group had good reliability of forward flexion and posterior extension,while the left and right lateral flexion reliability were mediocre.There was no statistical difference in left/right MM FI in the control group(p> 0.05).Correlation between bilateral MMFI and posterior extension in DSD group(r= -0.395),MMFI negatively correlated with VAS(r=-0.381),RDQ was negatively correlated with forward flexion and sagittal activity, respectively(r=-0.441,-0.425),Cobb angle is correlated with posterior elongation(r=0.372), TK was positively correlated with MMFI on the concave side(r=0. 460) and negatively correlated with forward flexion and sagittal activity(r=-0.406,-0.410),LL was positively correlated with FI on the concave side (r=0.412),TK/LL was negatively correlated with anterior flexion,sagittal mobility,and lateral flexion(convex side)(r=-0.424,-0.370,-0.576) Conclusion:DSD showed decreased LROM, increased MMFI and decreased RDQ. Reduced sagittal mobility and increased paravertebral muscle degeneration may mutually influence the quality of life in DSD, indicating that their mobility and paravertebral muscle degeneration should be comprehensively evaluated clinically.