A subwavelength ring-shaped three channels metal-insulator-metal waveguide demultiplexer is proposed. The transmission characteristics are investigated using finite-difference time-domain method from visible to near infrared spectrum. The multi order resonance phenomenon is found in the ring when the electromagnetic waves satisfy the resonance condition. The second, third, fourth order resonance waves can be separated by optimizing output ports next to the ring. Moreover, the resonance wavelengths of the ring can be controlled by setting the radius of the ring. The structure has light trapping and transmission functions, which can solve the modes separation transmission of signal. This design structure may be useful in optical integration and communication.