Sag control method for small-sag datum strand

The invention discloses a sag control method for a small-sag datum strand, inn order to solve the problems that the adjustment amount of the present cable length is too large in error under a small sag, or inconvenient to programme on the spot. The sag control method for the small-sag datum strand comprises the following steps of: acquiring the relationship between the adjustment amount of the cable length of a suspension cable and the change amount of a sag via a simplified adjustment cable formula based on parabola theory, and the unstressed length S0 of the simplified suspension cable; then calculating the adjustment amount Delta S needing to be adjusted, of the cable length after knowing a sag difference Delta f; and finally lengthening or shortening the Delta S at one end of a flexible cable, anchoring, and detecting that a mid-span elevation achieves a target elevation. Compared with a determination method for the adjustment amount of the cable length based on catenary theory and quasi-catenary theory,