Stretch forming process of aircraft skin over reconfigurable compliant tooling is a new technology in skin manufacturing. During this process, the coefficient of friction is important for modeling accurately the process of stretch forming. The objective of this research is to measure the coefficient of friction for aluminum alloy in contact with polyurethane rubber in reciprocal sliding. An orthogonal experimental design was used to reveal the impact of four factors on the coefficient of friction, including lubrication, normal load, aluminum alloy material and sliding velocity. It is shown that lubrication is a major factor, sliding velocity is a minor factor. The influence of normal pressure is less than sliding velocity and the influence of aluminum alloy material is not very obvious. Finally, based on the experiment results, the selections of lubricant and stretching velocity are discussed in order to improve the process of stretch forming.