A novel network-coding-based retransmission mechanism using chase combining mechanism for broadcast flows is presented. An information-theoretic performance bound is also developed to explain and predict the coding gains of the chase combining (CC) in network coding broadcast scheme using random coding bounding techniques. The core idea is to recover packets for individual receiver simultaneously using the network coding scheme and joint the soft information in each retransmission phase for packets not received correctly in the decoding process. Analytic results and simulation illustrate that the transmission efficiency can be sharply increased in the whole network especially in fairly severe fading circumstance. Moreover, complexity and overhead of the scheme is not added and a link from network coding to practical physical layer process (like channel coding and hybrid ARQ of chase combing) is established.