Terahertz communication, as an important research topic in the context of next-generation large-capacity wireless networks, is significant for constructing high-speed inter-satellite quantum communication networks. The inter-satellite terahertz continuous-variable quantum key distribution (CV-QKD) scheme based on Gaussian-modulated coherent states usually employs active modulation to prepare quantum states; namely, amplitude and phase modulators and a quantum random number generator (QRNG) are required. However, implementing high-speed active modulation with high extinction ratio and high stability is challenging in practice. Furthermore, the modulation format of active modulation is relatively complex and tolerates only small modulation errors, which hinders the construction of high-speed inter-satellite quantum communication networks. In view of the above analysis, this paper proposes an inter-satellite terahertz CV-QKD scheme based on passive state preparation, in which a thermal terahertz source, beam splitter, optical attenuator, and homodyne detector are used for passive modulation of quantum states. This approach eliminates the need for amplitude and phase modulators and a QRNG, effectively simplifying the implementation of the inter-satellite terahertz CV-QKD protocol. This paper analyzes the security and performance of the proposed protocol. Simulation results show that the performance of the proposed protocol improves significantly with increasing average photon number of the thermal terahertz source and quantum signal frequency, approaching the performance of the ideal Gaussian-modulated inter-satellite CV-QKD protocol. In addition, this paper provides a schematic diagram of the local oscillator system for the proposed scheme, analyzes its physical feasibility and existing technical implementation from a practical perspective, and offers a reference for constructing a low-cost and low-complexity inter-satellite quantum communication network.