There has been much interest in use of a tunable diode laser for absolute distance interferometry. We report on a novel method?using changeable synthetic wavelength chain (CsWC) to measure absolute length?based on a tunable diode laser. During the measurement, the desired synthetic wavelengths are calculated according to the distance to be measured and the measurement uncertainty. Then by tuning the wavelength of the laser, the desired synthetic wavelength chain is created. In addition, a differential measurement setup, which consists of two dual-beam interferometers, is proposed to test the feasibility of the CSWC method. The experiment results demonstrate that the CSWC method can work effectively. Although under present conditions a measurement uncertainty of only 3 x 10-5 is achieved, it is sufficient to design a differential optical probe.