A ultra-small micro-ring phase shifter based on the silicon-on-insulator (SOI) material is designed. 2π phase shift in the free spectral range and optimal linearization is achieved. According to the phase shift characteristics of the micro-ring resonator all-pass phase structure, phase shift of the micro-ring is π at the critical coupling area and 2π in the over coupling area. Two parameters (straight waveguide width and spacing) of the micro-ring are investigated which affect the phase shift. Finesse F also is used as a parameter for spacing, and micro-ring resonator’ phase shift combined with the power of change is discussed. The experimental results show that the designed micro-ring phase shifter can achieve the RF phase shift of 0～4 rad, and RF power variation is less than 6 dB with a 40 GHz RF signal.