Operations in assembling and joining large size aircraft components are changed to novel digital and flexible ways by digital measurement assisted alignment.Positions and orientations(P&O)of aligned components are critical characters which assure geometrical positions and relationships of those components.Therefore,evaluating the P&O of a component is considered necessary and critical for ensuring accuracy in aircraft assembly.Uncertainty of position and orientation(U-P&O),as a part of the evaluating result of P&O,needs to be given for ensuring the integrity and credibility of the result;furthermore,U-P&O is necessary for error tracing and quality evaluating of measurement assisted aircraft assembly.However,current research mainly focuses on the process integration of measurement with assembly,and usually ignores the uncertainty of measured result and its influence on quality evaluation.This paper focuses on the expression,analysis,and application of U-P&O in measurement assisted alignment.The geometrical and algebraical connotations of U-P&O are presented.Then,an analytical algorithm for evaluating the multi-dimensional U-P&O is given,and the effect factors and characteristics of U-P&O are discussed.Finally,U-P&O is used to evaluate alignment in aircraft assembly for quality evaluating and improving.Cases are introduced with the methodology. Operations in assembling and joining large size aircraft components were changed to novel digital and flexible ways by digital measurement assisted alignment. Positions and orientations (P & O) of aligned components are critical characters which assure geometrical positions and relationships of those components. Before, evaluating the P & O of a component is considered necessary and critical for ensuring accuracy in aircraft assembly. Uncertainty of position and orientation (U-P & O), as a part of the evaluating result of P & O, needs to be given for integrity the integrity and credibility of the result; further, U-P & O is necessary for error tracing and quality evaluating of measurement assisted aircraft assembly. However, current research mainly focuses on the process integration of measurement with assembly, and usually ignores the uncertainty of measured result and its influence on quality evaluation.This paper focuses on the expression, analysis, and application of U-P & O in measurement assisted align ment. The geometrical and algebraical connotations of U-P & O are. T, an analytical algorithm for evaluating the multi-dimensional U-P & O is given, and the effect factors and characteristics of U-P & O are discussed. used to evaluate alignment in aircraft assembly for quality evaluating and improving. Cases are introduced with the methodology.