A two-phase, rate-split, static nonorthogonal decode- and-forward protocol for the cooperative relay network consisting of a source, multiple half-duplex relays and a destination, all having single antenna, is proposed in this paper. In the proposed protocol, the desired transmission rate R is split into rates R1 and R2; then the source sends rate R1 during the first phase and rate R2 during the second. Explicit expressions for R1 and R2 are also given. It is shown that the proposed protocol achieves the optimal cooperative diversity derived from the information theoretic cut-set bound in high SNR regime. Compared to the compress- and-forward protocol, the proposed protocol is much simpler for practical implementation, holds the same for any number of relays and requires only local channel-state-information at each node, except for a small feedback of rate R1 as well as a selection index of relays.