Cooperative diversity technology has been recently proposed as a way to form virtual multi-antenna arrays that can be used to improve the performance of the wireless networks.The average level crossing rate and the average output duration are important index to judge system’s the second-order statisic character.An incremental amplify-and-forward relaying system with two relays（2R-IAF）is presented.Closed-form expressions for the outage probability are given.And the average level crossing rate and the average output duration of the 2R-IAF system are also presented.Results show that the normalization average level crossing rate and the average output duration are highly dependent on the choice of switching threshold and outage threshold.