We present a prototype of thermal interface material (TIM) by incorporating aligned carbon nanotube arrays (CNA) into polydimethylsiloxane (PDMS). The morphology of CNA was maintained by adopting in-situ injection molding method, and the nanotube-polymer composite film was obtained by curing the PDMS at room temperature. We applied steady-state methods to measure the thermal conductivity of this kind of nanocomposite. Comparing to the pure PDMS, the thermal conductivity of the composite was greatly increased, which can be attributed to the thermal conducting passages formed by vertical aligned carbon nanotubes from one side of the film to the other. We also managed to improve the thermal conducting performance of the composite by evaporating a 1-μm-thick aluminum film on the top of a raw CNA, which serves as a heat current collector to decrease the thermal contact resistance. The experiment results suggest these kinds of composites have broad application prospect for thermal management in the future.