The invention discloses a pressure bearing type fixed diameter anchor head or expanded head anchor rod prestress application method. Drilling is conducted to the design depth till rotary jet grouting or mechanical chambering construction can be developed, a pull rod of an anchor rod and a fixed diameter anchor head or an expanded head are placed, after the expanded head is arranged in place, the expanded head is expanded to the design size through an expanding mechanism, then, high-pressure grouting or concrete pouring is conducted, and pile forming is achieved in an expanded body section and a whole free section. Threaded steel bars to which prestress can be applied are adopted in the pull rod in the anchor rod, spiral stirrups and base bottom plate steel bars on a base are bundled, and collisions of the prestress steel bars are avoided in the bundling process. Lastly, a base concrete base bottom plate is poured by erecting a template.