In this paper, we analyze the outage probability of the full-duplex relaying (FDR) system with non-negligible residual self-interference (RSI). By investigating the signal-to-interference-plus-noise ratios (SINRs) at the relay and the destination, the exact expression of the outage probability for selective decode-and-forward (SDF) protocol is derived in closed-form over Nakagami-m fading channels. To get more insight about the effect of system parameters, we develop an asymptotic analysis on the outage performance. Our results show that the achievable diversity of SDF protocol depends on the shape factors of fading channels and the power scaling scheme of the relay. Moreover, we show that the SDF protocol achieves the best outage performance and is robust to the residual self-interference.