To decrease landing velocity of parafoil system and improve landing safety of payload, a method for determining the optimal flare landing altitude was proposed, and a study on the influencing factors and calculation models of relative flare landing altitude and landing velocity was completed. Firstly, a two-body nine-degree-of-freedom(DOF) dynamic model of the parafoil system and a coupled aerodynamic characteristic model of flare landing control were established, providing a more realistic simulation of the motion performance of the parafoil system under control between two bodies. The velocity and attitude changes of the parafoil system under flare landing control were studied, and the numerical results were consistent with the results in the literature, with a maximum error of 8.20% in glide ratio. Secondly, based on this model, with the minimum vertical landing velocity as the optimization objective, the optimal landing altitude was determined using the time dichotomy method, and the impact of flare maneuver timing on the landing velocity was analyzed. Then, simulation calculations were conducted on the optimal landing altitude under different initial conditions, wing load, landing altitude, and attack angle. The formula fitting of relative flare altitude and landing velocity was completed by the least squares method. It was found that the initial parameters have a minimal effect on the optimal landing altitude. As the wing load and landing altitude increase, the landing velocity and relative landing altitude also increase. The attack angle has a minor impact on the landing velocity, but an increase in the attack angle leads to an increase in the height of flare landing. The relative flare altitude and landing velocity calculation model proposed in this paper is in goof agreement with the numerical calculation results, with a maximum error less than 4.00%, indicating that the calculation model has good applicability.