Interference-fit riveting is a critical fastening technique in the field of aerospace assembly. Besides the basic connection performance as conventional riveting, interference-fit riveting also improves both the fatigue performance of rivet hole and the sealing performance of rivet joint. Both of the fatigue and sealing performance are determined by the interference-fit level of the rivet joint. The lower level of interference-fit causes the leakage way existing in the rivet joint, while the excessive level of interference-fit results in stress concentration around the rivet joint at where the initial cracks appearing. However, the conventional interference-fit level measurement methods are based on direct measurement by destructive test on test-piece, or indirect measurement by off-line dimensional measurement of upset rivet head. Each of the measurement methods goes against automatic riveting. An on-line non-destructive test method is developed for interference-fit level measurement in this paper. During the process of servo driving riveting combined with force measurement, the force-deformation data points of the deformed rivet can be on-line obtained. The extracted feature points from the force-deformation data points can represent the height of the upset rivet head. Combined with the algorithm for calculating the diameter of the upset rivet head based on the maximum riveting force, the volume of the upset rivet head can be obtained. Then, according to the law of volume constancy, the interference-fit level of the rivet joint can be on-line calculated. What’s more, to realize on-line calculation, an on-line data processing software is developed by Visual C++ and integrated into the HMI software of CNC system. Also, finite element simulation and an experiment are conducted to validate the feasibility and effectiveness of the proposed method. The results demonstrate the precision of the algorithms and the effectiveness of the on-line interference-fit level measurement method.