We demonstrate two methods to dynamically modulate the directional excitation of surface plasmons (SPs) in subwavelength slits structure by embedding nonlinear media or introducing oblique incidence. Finite-difference time-domain method simulation shows that the electromagnetic field intensity, patterned by the interference of two SPs waves along the exit interface, can be arbitrarily tailored by adjusting the phase difference between the two slits. The modulation of SPs has the potential application for all-optical SPs switch. (C) 2011 Elsevier GmbH. All rights reserved.