Abstract: The suspension cable structure with small sag-span ratio (less than 1/30) is adopted in the flexible photovoltaic support, and it has strong geometric nonlinearity. Taking the tension of the cable in the straight line state as the initial condition, the cubic equation and explicit analytic solution of the mid-span deflection under uniform distribution load are given, and the high precision approximate solution of the cable force considering large deformation geometric nonlinearity is obtained. By differentiating the equilibrium equation and the deflection equation, the vertical tangent stiffness of the equilibrium state is obtained. Compared with the results of nonlinear finite element analysis, the errors of mid-span deflection and cable tension are less than 0.5%. The static calculation formula obtained in the paper is simple and accurate, and the vertical tangent stiffness of equilibrium state has clear physical significance, which can provide reference for static analysis and structural design of flexible photovoltaic support.