GPGPU-powered supercomputers are vital for various science and engineering applications. On each cluster node, the GPU works as a coprocessor of the CPU, and the computing task runs alternatively on CPU and GPU. Due to this characteristic, traditional task scheduling strategy tends to result in significant workload imbalance and underutilization of GPUs. We design an adaptive scheduling strategy to alleviate such imbalance and underutilization. Our strategy proposes to logically treats all GPUs in the cluster as a whole. Every cluster node maintains a local information table of all GPUs. Once a GPU call request is received, a node selects a GPU to run the task in an adaptive manner based on this table. In addition, our strategy does not rely on a global queue, and thus avoids excessive internode communication overhead. Moreover, we encapsulate our strategy into an intermedia module between the cluster and users. Consequently, underlying details of task scheduling is transparent to users, which enhances usability. We validate our strategy through experiments.