The invention discloses functional ink. The functional ink is prepared from, by weight, 5-40% of a wetting agent for printing inks, 0.1-5% of a viscosity modifier, 0.1-10% of a surface active agent, 0.1-5% of a pH regulator, 0.1-5% of a complexing agent, 0.1-2% of bactericide, 0.1-30% of functional auxiliaries and the balance water. The functional auxiliaries are one or more of a rapid color developing agent, a fastness promoting agent, a penetrant, a softening agent, an antistatic agent, an anti-stiff finishing agent, an antibacterial finishing agent and a waterproof finishing agent. In addition, the invention discloses a printing method of the functional ink. The method comprises the steps that 1, before ink jet ink is used for jetting ink, the functional ink is used for performing pre-printing on a printing medium; 2, after the jet ink is used for performing ink printing on a printing medium, the functional ink is used for performing post-printing on the printing medium; 3, the functional ink and the jet ink are used for simultaneously performing at least one printing on the printing medium.