Recently Koy proposed primal-dual bases which have better quality than LLL-reduced bases in high-dimensional lattice
but his efforts did not take into account the low and upper bounds for the ratios of primal-dual bases to successive minima.In this paper some useful properties of Koy’s primal-dual bases are analyzed and then the low and upper bounds for the ratios of primal-dual bases to successive minima are introduced and proved.At the end
the Round-off algorithm for the approximate-CVP is improved using primal-dual bases and its result has a better approximation factor than L.Babai’s.