The invention discloses a numerical calculation method of internal force of a beam string structure. The method includes establishing a force bearing equilibrium equation set on the basis of the method of static equilibrium and section internal
force equilibrium, wherein the force bearing equilibrium equation set is an equation set about the equilibrium relation of a section
bending moment Mb of an upper-layered beam, a section shearing force Vb of the upper-layered beam, a section
axial force Nb of the upper-layered beam in an optional position with abscissa x of a beam string, a section
axial force T of a lower-layered cable, an entire section
bending moment Mx of the beam string and an entire section shearing force Vx of the beam string in an optional position with abscissa x of a beam string, among; figuring out an expression about the abscissa x of the beam string from the section
bending moment Mb of the upper-layer beam, the section shearing force Vb of the upper-layer beam, the section
axial force Nb of the upper-layer beam and the section axial force T of the lower-layer cable, by constructing an equation that external work W is equal to a sum of a
bending strain energy Ubn of the upper-layer beam, a compressive
strain energy Ubn of the upper-layer beam and a
tensile strain energy Ucn of the lower-layer cable, according to the principle of real work. By the aid of the method, the component
internal forces of the upper-layer beam and lower-layer cable of the beam string structure can be estimated and calculated rapidly and accurately, and data are supplied for section
bearing capacity checking.