The exploration of asteroids presents significant challenges due to their low gravity and irregular terrain. To address these issues, this study proposes a dynamic modeling framework for a flexible net system integrated with mobile detection unit, enabling a transition from passive capture to active detection. Notably, the system incorporates a multi-body dynamics model, accounting for the sliding contact between mobile detection unit (MDU) and the net, as well as the flexible coupling effects and gravitational perturbations inherent to small bodies. The Kelvin-Voigt model is employed to characterize the net’s tension via a spring-damping formulation, while a polyhedral method replaces traditional spherical approximations to minimize modeling errors. Furthermore, the MDU are treated as point masses sliding along the net’s line segments, with their motion states parameterized to derive kinetic equations encompassing elastic, damping, gravitational, contact, and frictional forces. Boundary transformation equations are introduced to facilitate autonomous transitions between adjacent line segments. The Eulerian method is adopted to numerically solve the dynamic equations, and the model is validated using asteroid 101955 Bennu as a case study. Results demonstrate that the MDU achieve stable locomotion across the net, including seamless transitions at endpoints, while maintaining dynamic stability and optimal detection coverage in weak gravity and complex terrain. Therefore, this framework not only advances the theoretical foundation for active surface exploration of small bodies but also offers practical insights for future deep-space missions.