In this paper, Using a 2D photonic crystal and a novel square ring resonator,several compact and simple structures have been introduced in the present paper toconstruct optical add/drop filters and multi-channel filter. The difference structures hasbeen designed and simulated by using the proposed square ring resonator and differentdropping waveguides. To do analyses, the finite-difference time-domain method and theplane wave expansion have been used. The three add/drop filters can separate thewavelength of 1554 nm with a transmission coefficient of 100 %, quality factor of 1295and bandwidth of 1.2 nm. The models of structures are simulated by the RSOFT CADLayoutsoftware. The results, flexibility and simplicity of structures have caused fromtheir used to designing of an optical multi-channel filter with a channel spacing of 1.5nm. The advantages of this design include the channel spacing, quality factor,transmission coefficient and bandwidth which are suitable for applicability in opticalcommunication systems such as wavelength division multiplexing systems.