A needle-free medicine injection connector, comprising: a covering part with an injection port, a positioning notch and a groove configured on an out surface of the covering part; a connecting part with an inner cavity, the cavity having a bottom, a piercing passage defined through the connecting part, a hole defined at the bottom, the connecting part having a positioning projection for engagement with the groove of the covering part, wherein the connecting part has a protruding part for engagement with the positioning notch of the covering part for preventing the connecting part from slippage or coming off when a syringe is attached with the injection port; a valve unit installed in the cavity of the connecting part, the valve unit comprising a piercing conduit member and a resilient valve composed of a top half valve and a bottom half valve, wherein the top half valve has a first resilient part, one end of the first resilient part has a top surface, a top slit is defined on the top surface of the top half valve, the top surface of the top half valve has a rim for sealing the injection port, the other end of the first resilient part has a first engaging portion having a first passage defined therethrough and communicating with the top slit, the first engaging portion of the top half valve has a first mounting part; the bottom half valve has a second resilient part, one end of the second resilient part has a base, a bottom slit is defined on the base of the bottom half valve, the other end of the second resilient part has a second engaging portion having a second passage defined therethrough and communicating with the bottom slit, the second engaging portion of the bottom half valve has a second mounting part; the piercing conduit member is installed between the top half valve and the bottom half valve, the piercing conduit member has a main positioning part disposed between a first engaging portion of the top half valve and a second engaging portion of the bottom half valve, a flow passage is defined through the piercing conduit member, the flow passage has an opening at both ends thereof, a first opening at one end and a second opening at the other end thereof, the second opening is connected to the hole of the bottom of the connecting part the injection connector having at least one air vent, characterised in that the at least one air vent is an elongate slot through the wall of the covering part, the air vent extending between the groove and the positioning notch and being aligned with a concave track of the covering part, in that the slot extends in the direction of movement of the piercing conduit member, and in that the air vent extends to both sides of the main positioning part. a covering part with an injection port, a positioning notch and a groove configured on an out surface of the covering part; a connecting part with an inner cavity, the cavity having a bottom, a piercing passage defined through the connecting part, a hole defined at the bottom, the connecting part having a positioning projection for engagement with the groove of the covering part, wherein the connecting part has a protruding part for engagement with the positioning notch of the covering part for preventing the connecting part from slippage or coming off when a syringe is attached with the injection port; a valve unit installed in the cavity of the connecting part, the valve unit comprising a piercing conduit member and a resilient valve composed of a top half valve and a bottom half valve, wherein the top half valve has a first resilient part, one end of the first resilient part has a top surface, a top slit is defined on the top surface of the top half valve, the top surface of the top half valve has a rim for sealing the injection port, the other end of the first resilient part has a first engaging portion having a first passage defined therethrough and communicating with the top slit, the first engaging portion of the top half valve has a first mounting part; the bottom half valve has a second resilient part, one end of the second resilient part has a base, a bottom slit is defined on the base of the bottom half valve, the other end of the second resilient part has a second engaging portion having a second passage defined therethrough and communicating with the bottom slit, the second engaging portion of the bottom half valve has a second mounting part; the piercing conduit member is installed between the top half valve and the bottom half valve, the piercing conduit member has a main positioning part disposed between a first engaging portion of the top half valve and a second engaging portion of the bottom half valve, a flow passage is defined through the piercing conduit member, the flow passage has an opening at both ends thereof, a first opening at one end and a second opening at the other end thereof, the second opening is connected to the hole of the bottom of the connecting part the injection connector having at least one air vent, characterised in that the at least one air vent is an elongate slot through the wall of the covering part, the air vent extending between the groove and the positioning notch and being aligned with a concave track of the covering part, in that the slot extends in the direction of movement of the piercing conduit member, and in that the air vent extends to both sides of the main positioning part.