The modeling of the stratosail of a stratospheric satellite includes both the modeling of a flexible tether and that of a rigid stratosail body, thus being a complicated and flexible-rigid coupled modeling process. This paper analyzes the stress of the stratosail and calculates the size and direction of the tensile force of the tether in different states in accordance with the moment-equilibrium principle. It analyzes the effects of the gravity, aerodynamic force and tensile force of the tether on the stratosail and calculates the inclination angle, deviation angle and tensile force of the tether at its different attitude angles. The analysis of the calculation results shows that the absolute values of the inclination angle and deviation angle of the tether increase as increasing absolute value of its yaw angle, that the lateral tensile force components of the stratosail increase but that the resultant tensile force of the tether does not increase but decreases slightly. The modeling of the stratosail of a stratospheric satellite includes both the modeling of a flexible tether and that of a rigid stratosail body, thus being a complicated and flexible-rigid coupled modeling process. This paper analyzes the stress of the stratosail and calculates the size and direction of the tensile force of the tether in different states in accordance with the moment-equilibrium principle. It analyzes the effects of the gravity, aerodynamic force and tensile force of the tether on the stratosail and calculates the inclination angle, deviation angle and tensile force of the tether at its different attitude angles. The analysis of the calculation results shows that the absolute values of the inclination angle and deviation angle of the tether increase as increasing absolute value of its yaw angle, that the lateral tensile force components of the stratosail increase but that the resultant tensile force of the tether does not increase but decreases slightly.