A hydraulic paint sprayer cylinder is provided to prevent deformation of a hydraulic paint sprayer and the generation of inner spool and to ensure excellent abrasion resistance. A hydraulic paint sprayer cylinder comprises a lower block(35) raising a piston according to the hydraulic pressure operated upward by supplying hydraulic oil inside a hydraulic paint sprayer cylinder; an upper block(3) descending a piston according to the hydraulic pressure operated downward by supplying hydraulic oil inside a hydraulic paint sprayer cylinder; an inner spool(11) moving upwardly and downwardly depended on the movement of the piston while being rotated inside the hydraulic paint sprayer cylinder; a valve rod(29) playing a support as a role when the inner spool rotates at the upper space of a piston; a piston nut(24) having grooves passing through the valve load and a screw thread; a spring(30) giving the rebound to the piston in turning the up and down movement of the piston; and a bolt(1) for the cover.
