X-ray Talbot-Lau interferometer, offering multi-contrast for the imaged objects, has shown powerful capacity in imaging biological soft tissues, low density materials, etc. However, the length of the system is constant, which limits its applications. Here, we establish a new X-ray Talbot-Lau interferometer theory to achieve a flexible phase contrast imaging system. This interferometer has a tunable length-scale scattering sensitivity. The experiments show that we can regulate the scattering signal individually. Furthermore, we construct a G2-less phase contrast imaging based on this flexible interferometer to validate the possibility of highly compact X-ray Talbot-Lau interferometer.