Decentralized approaches for Web services discovery, such as peer-to-peer, become more and more attention - getting in the scientific community. In this paper, we propose a peer-to-peer framework, which adopts an enhanced skip graph named Servicelndex as the overlay network for service discovery. To guarantee discovery efficiency, Servicelndex schemed WSDL-S (Web services semantics) as semantic Web services description language and extracted its semantic attributes as indexing keys in skip graph. Also a multi-layer P2P overlay network was constructed to aggregate similar keys and keep load balancing on peer nodes. The evaluation showed that the Servicelndex system performs considerable service discovery efficiency.