In layered P2P streaming system, how to allocate number of the copies for each layer is a challenging problem. In this paper, we present a substream allocation scheme in layered P2P streaming. The proposed allocation scheme is adaptive to the request rate and number of the qualified peers. The simulation results show that the proposed allocation scheme enables the system to achieve an overall better quality compared to the general allocation schemes with fixed allocation percentages. In addition, the proposed allocation scheme can accelerate the growth of peer population in the initial stage of hybrid P2P streaming systems.