An ultra-wideband and high precision 6-bit phase shifter operating at 5-20 GHz was designed in SMIC 40 nm CMOS technology. The phase shifter was implemented through vector modulation and mainly consisted of input baluns, orthogonal signal generators, vector modulators, and digital to analog conversion circuits. For orthogonal signal generator, a three-stage poly-phase filter structure was designed to improve the bandwidth. A low error structure and current array control scheme were designed to reduce the phase error of the vector modulator. The post simulation results show that the input and output return loss are less than 8.85 dB and 10.12 dB respectively, the RMS phase error is less than 1.52°, and the RMS gain error is less than 0.17 dB. Under 2.5 V supply voltage, the power consumption is 43.50 mW. The chip size is 1.06 mm ×0.80 mm.