In order to solve the time consuming problem tracing surface quality problem of complex curved parts machined by fiveaxis NC machine tool,the surface quality test piece was designed.The decoupling optimization method of part surface quality problem based on specimen was studied,the decoupling mapping from electromechanical coupling characteristic of machine tool to surface quality test part was established,and the rapid traceability of the surface quality problem of parts was realized.Combined with the mechanical adjustment and control parameter setting method of weak stiffness link,the surface roughness of the parts is reduced from Ra1.6~ 3.4 μm to Ra0.8 μm,and the surface quality is improved effectively.