The invention discloses a calculation method of bending resistance bearing capacity of a normal section of a circular cross section fender post after partial fracture. The calculation method comprisesthe following steps that step 1, discretely and uniformly distributed steel bars in the fender post are equivalent to continuous steel rings with an equal thickness, and the thickness t of the equivalent steel rings is calculated; step 2, a equilibrium equation of resultant compressive stress D of section concrete and tensile force Dof section steel bar is established, and the height coefficient epsilon of a section compressive zone of the circular cross section fender post after the partial fracture is calculated according to the equilibrium equation; and step 3, the bending resistance bearing capacity M of the remaining section of the circular cross section fender post after the partial fracture and the bending resistance bearing capacity M of the steel bars are calculated, and finally the bending resistance bearing capacity M of the normal section of the circular cross section fender post after the partial fracture is calculated, and M=M+M. The calculation method is clear in thinking and reliable in results, can be used for safety analysis of structures of the circular cross section fender post after the partial fracture in the actual engineering, and provides a direct reference for the safety evaluation of a foundation pit under similar conditions and further treatment methods, and improves engineering safety factors.