Metagenomic information provides deeper understanding of the ecological role, metabolism, and evolutionary history of microbes in a given ecosystem by analyzing environmental DNA directly without prior cultivation. In this paper, we propose methods and implement tools and web services to facilitate the bioinformatics analysis of metagenomic data. The open-source metagenomic sequences data analysis softwares and Hadoop Map/Reduce framework were integrated to construct accessible cloud platforms for metagenomic data analysis. The functionality of the platform is examined by composition analysis of human oral microbiome. The metagenomic analysis tools on cloud platforms are accessible by users through the web services with corresponding virtual machine images provided.