We introduce a modified surface plasmonic waveguide with an arc slot. The dependences of distribution of energy flux density, effective index, propagation length and mode area of the symmetric mode supported by this waveguide on geometrical parameters and working wavelength are analysed by using the finite-difference frequency-domain (FDFD)method. Results show that the energy flux density distributes mainly in four coers which are formed by two arcs, and the closer to the coers it is, the stronger the energy flux density will be. The effective index, the propagation length and the mode area are influenced by geometrical parameters, including the width, the thickness and the arc radius of the surface plasmonic waveguide, as well as the working wavelength. It has been shown that the surface plasmonic waveguide with an arc slot has better propagation properties than the surface plasmonic waveguide with a straight slot.This work may be helpful for applying the slot surface plasmonic waveguide to integrated photonics.