The invention discloses a manufacturing method for a hexagonal seamless tube. The manufacturing method comprises the following specific steps that firstly, cold rolling processing is conducted, specifically, a blank is subjected to at least two times of cold rolling to complete manufacturing of a middle round tube; secondly, heat treatment is conducted, specifically, the middle round tube is heated and then subjected to heat preservation; and thirdly, forming cold rolling is conducted, specifically, the formed tube with the outer contour of the radial cross-section and the inner hole contour both being hexagons is formed by rolling through a cold rolling process combined with a plurality of processing rollers. Stainless steel and the alloy hexagonal seamless tube which are high in dimension precision, good in surface quality and homogeneous and stable in performance can be successfully manufactured.