The demand for secure and reliability transmission has heightened dramatically with the rapid development of hybrid terrestrial-satellite communication networks. The satellite relay communication is an essential technique to solve the issue above. In this paper, a joint spatial-power resource allocation scheme (SPRAS) is proposed to enhance the covertness of terrestrial-satellite communication system under the promise of high reliability and unpredictability of relay selection patterns. Specifically, a joint transmit power and relay direction selection optimization problem is constructed to maximize the warden's detection error probability, with transmission reliability and relay selection uncertainty as constraints. The block coordinate descent algorithm is used to solve the formulated optimization problem. Numerical results demonstrate the superiority of our proposed SPRAS, which can obtain high reliability and covertness simultaneously.