Abstract: An injection syringe is used to assemble a needle thereon. The injection syringe has a syringe body, a needle base assembled inside the syringe body, and a pusher for pushing medicine. The syringe body forms first protrusions proximate an end and on an inner surface thereof. The needle base forms second protrusions on an outer surface thereof for cooperating with the first protrusions to engage or disengage the syringe body and the needle base. The needle base includes a needle connecting portion for connecting the needle, and a bugle-shaped bugle portion expands far away from the needle connecting portion. At least two ribs are formed on an inner surface of the bugle portion. A flange is formed at an end of the bugle portion. The pusher forms guiding posts, each guiding post having an inclined surface at an end thereof for abutting the flange. At least an abutting projection is formed on a top end of the pusher for biasing against the bugle portion.