An auto-retractable blood collection needle, including: a needle holder including a first tube, a second tube and a holder tail； a needle in stalled in the first tube； a built-in sliding sleeve which is elongated and through and has a C-shaped cross section； a needle shield which is hollow and elongated； and a spring sheathed on the first tube. The second tube is installed in the built-in sliding sleeve and is capable of sliding back and forth. The built-in sliding sleeve is installed in the needle shield and is capable of sliding back and forth. A locking mechanism is formed by the holder tail and the needle shield. When the holder tail is unlocked from the needle shield, a force of the spring pushes the second tube to slide backward, and then the built-in sliding sleeve is driven to slide rearward to lock with the needle shield.
