With the current generalisation of parallel architectures arises the concern of applying formal methods to parallelism. The complexity of parallel, compared to sequential, programs makes them more error-prone and difficult to verify. Bulk Synchronous Parallelism (BSP) is a model of computation which offers a high degree of abstraction like PRAM models but yet a realistic cost model based on a structured parallelism. We propose a framework for refining a sequential specification toward a functional BSP program, the whole process being done with the help of the Coq proof assistant. To do so we define BH, a new homomorphic skeleton, which captures the essence of BSP computation in an algorithmic level, and also serves as a bridge in mapping from high level specification to low level BSP parallel programs.