In this paper, we propose a terrestrial-satellite network (TSN) architecture to integrate the ultradense low earth orbit (LEO) networks and the terrestrial networks to achieve efficient data offloading.In TSN, each ground user can access the network over C-band via a macro cell, a traditional small cell, or a LEO-backhauled small cell (LSC). Each LSC is then scheduled to upload the received data via multiple satellites over Ka-band. We aim to maximize the sum data rate and the number of accessed users while satisfying the varying backhaul capacity constraints jointly determined by the LEO satellite based backhaul links. The optimization problem is then decomposed into two closely connected subproblems and solved by our proposed matching algorithms. Simulation results show that the integrated network significantly outperforms the non-integrated ones in terms of the sum data rate. The influence of the traffic load and LEO constellation on the system performance is also discussed. the core network via the traditional backhaul and LEO-based backhaul, respectively. Benefited from the UD-LEO constellation, we assume that each TST is allowed to connect to multiple satellites simultaneously [8], [11], thereby improving the resilience to the frequent handover of satellites [12]. Deployed by the same operator, all cells share the same C-band frequency resources for terrestrial communications. Multiple TST-satellite backhaul links over Ka-band are scheduled for each LSC. The network aims to maximize the sum rate of all users and accommodate as many users as possible. Therefore, the user association and resource allocation of multiple cells should be optimized subject to the backhaul capacity constraint of each cell. At the same time, the backhaul capacity of each LSC also needs to be maximized via the satellite selection and resource allocation. Various techniques have been considered for traffic offloading in the heterogeneous networks, such as satellite access [13], [14], hybrid satellite-terrestrial relaying [15]-[17], deviceto-device (D2D) multi-cell interference management [18]-[20], and cloud radio access. In [13], the terrestrial-satellite backhaul network shares the Ka-band and the terrestrial wireless links deploy the hybrid analog-digital transmit beamforming to mitigate interference. In [14], a single satellite covers a large area and the integrated terrestrial-satellite networks perform the cloudbased resource allocation. In [15]-[17], a hybrid terrestrial-satellite network sharing the same spectrum has been considered where either the satellite serves as a relay for one terrestrial sourcedestination pair or a terrestrial node relayes for the satellite -user pair. The average symbol error rate has been derived and the analytical diversity order has been obtained. In [18], [19], the D2D underlaying dense network has been considered and a distributed algorithm has been proposed to cope with the strong intra-cell and inter-cell interference. In [20], energy-efficient user association and resource allocation has bee...