Abstract: It is essentially impossible to apply the delimbing shears to timber production by simply amplifying the shears curve of the widely used branch-pruner. This paper provides a theoretical analysis based on the principle of force-saving sliding cutting. It is found that the blade edge curve of delimbing shears should be a logarithmic spiral for the sake of force saving. This curve would also improve the de-limbing quality. The value of ρ1 and ρ2 of the curve is relevant to the diameter of tree branch cut, material of the blade and the mounting dimension of the blade.