Abstract: In order to investigate the combined effects of bolt-hole interference fit condition and clamping force on the strength of the bolted mechanical composite joints and their mechanism, a finite element model validated by experiments was taken out. A three dimensional nonlinear finite element model agrees well with two sets of composite-to-titanium single-lap bolted joints tensile tests. Based on the finite element model, seven interference fit conditions combined with six clamping force conditions, altogether forty two different working conditions were studied. The results show that, although certain interference fit condition and clamping force may cause some pre-failure of the joints area, they can improve the contact condition and prevent failure evolution under bigger load, making the joints strength maximize. At the same time, there is interaction between interference fit and clamping forces on the joints strength, namely the optimal clamping force will be different under different interference fit conditions, vice versa. So the two factors on the interference fit and clamping force need to be considered at the same time in order to achieve the optimal structural design.