The present invention relates to a fluid injection needle unit having a function of preventing needlestick injury and infection wherein a cover, a needle body and a body are improved in shape, and after the needle body is inserted into a blood vessel of a patient, the cover is coupled to the bottom end periphery of the body and the needle body is detached from the body by means of detachable mounting members, so that a needle and the needle body are inserted unitarily into the cover to prevent the occurrence of the needlestick injury and infection.