Recently, a superconducting transition was found in silane in high-pressure experiments. However, the experimental x-ray diffraction (XRD) patterns do not match any one of the proposed silane structures, and it has been suggested to be originated from a platinum hydride. Here the underlying physics behind the anomalous superconducting transition in experiment is revealed by first-principles calculations. We predict a stable hexagonal P63/mmc phase of platinum hydride at high pressure. Its lattice constants and simulated XRD pattern are in excellent agreement with the experimental results. The superconducting transition temperatures in this phase are found to agree with the measured values, too. This discovery provides insights into the unusual superconducting behavior reported for silane.