An improved safe and convenient disposable automatic lancet, comprising a housing (1), a needle core (2) and a spring (3), in which: the needle core (2) is provided with a needle body (14) having a needle tip (7)； a housing (1) defines an ejection chamber (5), in which the needle core (2) is located, in which the needle core (2) has an end provided with a protective bar (4) ) and another end on which the spring (3) is fixed, the protection bar (4) has one end that projects from a needle ejection hole (6) and another end detachably connected to the core of the needle (2)； The housing has an elastic arm (8) that extends into the ejection chamber (5) to block the needle core (2), a bayonet (9) is provided on the needle core (2) , in correspondence with one end of the elastic arm (8), and the end of the elastic arm (8) elastically fits the bayonet (9), in which the housing (1) is provided with a firing button (10) which it has a first pressure leg (11) and a second pressure leg (19), both legs are inserted in the ejection chamber (5), in which in a state about to launch, the distance between the second leg of pressure (19) and the needle tip (7) is less than the distance between the first pressure leg (11) and the needle tip (7)； the first pressure leg (11) is close or contacts the end of the elastic arm (8)； and the second pressure leg (19) is provided with a tongue (12), in correspondence with which a self-locking hook (13) is provided on the housing (1)； the self-locking hook (13) is positioned in the downward pressure path of the tongue (12), when the second pressure tongue (19), together with the tongue (12) provided above, is pressed down, the tongue (12) and the self-locking hook (13) form a self-locking adjustment； a pressure channel (17) down is left in the ejection chamber (5) along the pressure path below the second pressure leg (19)； the protection bar (4) is provided with a safety sleeve (20), and when the protection bar (4) is mounted, the safety sleeve (2
