Abstract: This paper proposes a comprehensive modeling method for echo signal simulation of high-speed moving targets in bistatic wideband radar systems. In spaceborne bistatic radar scenarios, the targets are typically high-speed aerial objects. Traditional "stop-and-go" models fail to account for intra-pulse motion effects and dynamic scattering characteristics, leading to inaccurate echo simulation. To address this issue, a time-varying geometric model that considers changes in target position and orientation is introduced. The radar echo is modeled as a response modulated by phase variations caused by target motion and scattering properties. Based on the generated time-domain echo of moving targets under this modulation, the echo signals and corresponding high-resolution one-dimensional range profiles can be accurately simulated. The effectiveness of the proposed method is validated through simulations, which exhibit noticeable peak shifts, mainlobe broadening, and amplitude fluctuations caused by intra-pulse motion and bistatic angle variations. These effects highlight the necessity of jointly considering motion and scattering modulation in practical radar signal modeling, providing a foundation for improving detection, imaging, and recognition performance based on target echoes and range profiles.