The Dynamic Partial Reconfiguration function of reconfigurable devices permits tasks to be performed simultaneously on a single device. Nevertheless, task placement and resource management problems emerge with the parallelism of reconfigurable devices. Traditional task placement algorithms are based on the assumption of a homogeneous architecture and simplify the task as a rectangular shape, which inevitably results in internal unused areas, thereby wasting a significant amount of programmable resources. To address the resource waste that comes with the assumption of a rectangular task shape and improve the placement quality, we adopted an interval list set to manage available programmable resources for a heterogeneous reconfigurable device and proposed an interval-based placement algorithm combined with a low-fragmentation selection strategy targeting the placement problem of multi-shape tasks. The efficiency of the proposed approach is proved theoretically, and simulation results demonstrate that the rejection ratio is decreased by at least 8.9% with an average fragmentation reduction of 18.1%.