The programming is still a challenging issue for the high performance distributed computing (HPDC) platform, and it is critical to the popularity of peer-to-peer (P2P) based HPDC systems. Therefore, this paper focuses on the design and implementation of OMP, a one-sided message passing programming model for unstructured P2P computing system, P2HP. Based on tasks' execution flow, P2HP provides a one-sided point-to-point message-passing communication library, and a software development kit with rich APIs for applications' parallelization. Furthermore, a serial sequence alignment algorithm is parallelized with OMP in P2HP. The evaluation shows that OMP makes P2HP practical and efficient.