Abstract-An optimal secure transmission scheme of space data is designed by optimizing the secure distribution of the space observation data in view of the change of source-channel condition. Various source-channel models are built based on the optimization objective of data quality, and then the data protection strategy and approach based on joint source-channel and secure coding are proposed. A quality evaluation and distribution model of space observation data is established, and the secure distribution of space observation data under separated source-channel coding and the encryption-authentication distribution of space observation data under joint source-channel coding are optimized and evaluated. The algorithms are analyzed and simulated. The data protection strategy and approach are validated in robustness, scalability and reliability.