The SiGe material system demonstrates the advantages of device fabrication and performance, also the unique characteristic of Ge/SiGe multi-quantum well structure expends the application range. A design of optical integrated phase modulator based on asymmetric Ge/SiGe coupled quantum well (CQW) was proposed in this paper. According to comprehensively analysis of asymmetric Ge/SiGe CQW structure by numerical simulation, the theory was verified by implementing the fabrication and measurement. It indicates that the maximum electrorefractive index variation up to 0.01 can be achieved by using the designed asymmetric CQW, while the applied electrical field exceeds 40 kV/cm at wavelength of 1450 nm. Moreover, the fabricated device attains the electrorefractive index variation 2.4×10-3 with 1.5 V reverse bias voltage and optical wavelength 1530 nm, and the corresponding VπLπ is as low as 0.048 V·cm. The asymmetric Ge/SiGe CQW phase modulator exhibits superior performance in the same type of modulators based on SiGe, and offers new opportunities to further development of optical integrated silicon modulators.