Here, interconnection technique to link digital microfluidic chips is proposed. Three kinds of digital microfluidic modules with connecting interface, including flexible module and two types of connector modules, are designed and fabricated. Since these modules are fabricated on a compliant polymer-based substrate (ITO PET), chip-to-chip droplet transportation even at different planes can be achieved by the proposed technique. A low-temperature fabrication process is developed for the polymer substrates, where the SU-8 acts as the insulator. Droplet transportation through electrowetting on curved surface is confirmed by testing on the bended flexible modules with different curvatures from 0 to 0.06 mm-1 at around 70 VAC. Then the droplet transportations between flexible and connector modules are investigated. It is found that the gap size between two modules and the sidewall profiles at interface affect the droplet transportation directly. For the gap size around 50μm with a smooth perpendicular sidewall profile, 80 VAC is shown to actuate droplet of 1.5 μl, 2.5 μl, or 3.5 μl to cross over the interface successfully.