By utilizing the self-collimation and co-directional coupling mechanism, an arbitrarily bent beam splitter is designed and analyzed theoretically,which is composed of a self-collimation zone,a coupled zone and two periodic dielectric waveguides. Dispersion relation in the coupled zone is analyzed theoretically using plane-wave expansion method, and the coupled length is calculated. The transmission character of electromagnetic wave in splitter is simulated by finite-difference time-domain simulations, and the steady electric field distribution is obtained. Effective coupling technique of coupling lightwave from self-collimation zone to coupled zone is discussed.The result shows that if the phase matching conditions are satisfied the light can be injected into the coupling section and transferred into the two output branches efficiently, the angle can be bent to arbitrary value, and the transmittance is above 90%. A new method which enlarges the distance of point source and image point based on the designed splitter is proposed.