Spiral surface plasmon (SSP) modes on uniform and tapered silver nanorods are explored by performing both simulations and theoretical analyses. On a uniform nanorod with a radius equal to 240 nm, the SSP modes can be generated by linearly superposed higher-order HE 1 and HE 2 eigenmodes. Both the single-and triplestranded SSP modes are produced by controlling the relative rotation direction of the two component modes. On a tapered nanorod, the spiral pitch of the SSP mode decreases with the reduction of nanorod radius. However, the field energy density along the nanorod axis increases to a maximum value and then falls.