The invention provides a door and window sash positioning device used for a sliding door and window. The sliding door and window comprises a door and window frame and a door and window sash, wherein the door and window sash is embedded and connected onto upper and lower frame guide rails of the door and window frame by upper and lower frame grooves; the door and window sash positioning device is mainly composed of a positioning fixing block and a positioning block cover plate; the positioning fixing block is fixed at the lower end part of the upper frame guide rail of the door and window frame through a nut and the outer side of the positioning fixing block is connected with one positioning block cover plate; the positioning fixing block and the positioning block cover plate are combined and then are embedded and connected into the upper frame groove in the door and window frame; the positioning fixing block is fixed on the position of a side angle part of the upper frame guide rail of the door and window frame; screw holes are formed in the middle of the lower end part of the positioning fixing block and cover plate positioning groove holes are formed in the two sides of the screw holes; the positioning block cover plate is embedded and connected into the cover plate positioning groove holes formed in the positioning fixing block through a positioning bulge and is connected with the positioning fixing block. The door and window sash positioning device used for the sliding door and window has the characteristics of simple structure and convenience for utilization and installation, and the shaking problem of the door and window sash can be solved very well.