Supervision on geotechnical investigation, which is different from the supervision on construction or design, is still in its beginning and being groped in China. The geotechnical investigation of metro engineering is more complicated and often calls for special requirements. therefore its supervision is more necessary. Taking the supervision on Nanjing metro project, the paper discusses the objectives, bases, procedure and main tasks of supervision on geotechnical investigation of metro engineering, and analyses its characters, principles should be followed and key points.