Using flexible net to capture space debris is more preferable than using rigid mechanisms. However, it is extremely difficult to deal with unconstrained and nonlinear flexible system. In this paper, space net capture system is designed, Based on finite element method, using ANSYS/LS-DYNA to simulate dynamic process of capture net. Analyzing casting angle, casting velocity, elastic modulus and cross section radius how to affect deploy of capture net, which is evaluated by maximum deploy area, deploy time, effective time, distance of deploy, and effective distance. Impact between space debris and net body is simulated and analyzed. The result shows that capture net gains better error tolerance from optimal casting angle and velocity. And increasing cross section radius and elastic modulus can enhance anti-impact of net body, but error tolerance will be worse, so choosing its value must be careful.