We propose a new scheme to form a surface Y- or X-shaped beam splitter for optically wave-guided atoms (or molecules) and its Mach-Zehnder interferometer by using the combination of a binary π phase plate and a micro-cylindrical lens. The physics idea and basic principle of our beam splitter are introduced, and the analytic relationships between the intensity distribution (or the intensity gradient, or the splitting distance, and splitting-path width) and the parameters of our optical system are derived and discussed. The potential applications of the beam splitter and its experimental feasibility are discussed. Our study shows that the design is novel and the scheme is simple, and it can be used to construct various integrated atom- (or molecule-) optical elements with surface micro-structures, and even to form some all-optically integrated atom (or molecular) chips.