Using the two-dimesional finite-difference time-domain (FDTD) method, the dependence of the reflectivity, the transmission rate and the energy splitting ratio, on the geometrical parameters of two kinds of Y-splitter with sine shaped arc and circular shaped arc, based on mental-insulator-mental (MIM) surface plasmonic waveguides, are analysed. Results show that the transmission characteristics of the two Y-splitters depend obviously on the parameter of the width of the waveguides and weakly on the two parameters of the offsets of the two output branches and the lengths of the curves. The transmission characteristics of the Y-splitter whose curves are circular arc-shaped are better than the Y-splitter whose curves are sine arc-shaped within 600~1500 nm. For asymmetrical Y-splitter, the reflectivity, the transmission rate and the power splitting ratio are affected obviously by the parameter of offset when the curves are sine arc-shaped and the energy splitting ratio can be up to 2∶1. The reflectivity, the transmission rate and the power splitting ratio are affected faintly by the parameter of offset when the curves are circular arc-shaped.