A new structure of tunable single micro-ring with three coupling points was proposed in the present paper based on the theory of coupled modes and transmission matrix. Also, the output optical spectrum was simulated by the aid of Matlab. In this new structure, we use silicon-on-insulator (SOI) as its material, so the output optical spectrum can be tuned when the length or temperature is changed in feedback waveguide. According to the outcome of simulation, when the coupling coefficient k is 0.018, the free spectral range (FSR) approaches 43.8 nm and the quality factor is 1.25×105. This resonator not only has narrow bandwidth, high quality factor and large FSR, but also can achieve the tunable output optical spectrum through modulating the properties of feedback waveguide. The corresponding curve was presented in this paper as well.