As the demand of mobile services for high bandwidth grows, aggregation of various wireless network resources in hybrid communication system becomes a trend. Network coding has been widely studied to solve the packet reordering, low aggregation efficiency problems which are brought by network heterogeneity. Even if the determination of coding scale is the core issue of network coding, current research can not adapt to heterogeneous wireless channels, resulting in low bandwidth aggregation and decoding efficiency. Therefore, we propose a cross-layer network coding scheme called Delay Determined Group Size (DDGS) scheme, which adaptively adjusts the coding scale to solve the problem of overall performance degradation caused by heterogeneous characteristics of wireless channels. It can get the utmost out of the performance improvement brought by network coding, to better avoid packet reordering as well as reduce the receiving delay at the receiving end. The simulation results show that DDGS is significantly superior to network coding schemes in existing state-of-the-art solutions.