In this letter,the physical layer security of hybrid automatic repeat request with chase combining (HARQ-CC) scheme is investigated from the viewpoint of information theory.Different from the literature which used Wyner code,our analysis focuses on the general scenario without specific code.We firstly obtain the outage probability of both main channel and wiretap channel.Since retransmissions are completely determined by main channel,we then prove that its achievable diversity order equals to maximum transmission number (K) while this order of wiretap channel is only one.Furthermore,we evaluate the metric of secure gap which demonstrates the difference between main channel and wiretap channel with reliable and secure constraints.As K increases,the secure gap decreases monotonously.When K is large enough,the security can be guaranteed even if wiretap channel is better than main channel.