An extension positioning structure for a portable memory device comprises a main body in a shell. A first end of the main body is disposed a drive element, and a spring is mounted outside a second end of the main body. A positioning element is pivotally disposed between the shell and the drive element. The positioning element includes a pivot shaft and an engaging portion. The engaging portion is helically formed with multiple cutting surfaces, and the positioning block is formed with a positioning block and a limiting block. By pushing the drive element, the cutting surface of the engaging portion of the positioning element cooperates with the positioning block and the limiting block to make the connecting terminal extend out of and retract into the shell, facilitating the operation and storage of the memory device while reducing both the production cost and increasing the yield rate.