An ultra-high sensitivity dual-gated biosensor based on an MOS transistor, which is applicable to detection of a series of early tumors. The sensor is prepared and processed by using SOI wafers, and a unique dual-gated structure is realized by ion implantation technique. The sensor is prepared by an ultraviolet lithography combined with an NLD etching method, realizing trace, instant and marker-free detection of tumor markers. The method detects a change in capacitance in the channel during binding of antigen antibodies. The detection method involved in the invention is more stable and strong in anti-interference, can meet the demands in the aspect of detection range and sensitivity, and especially has extremely outstanding detection sensitivity, and can detect a sample with a lowest concentration in the range of 1 fg/ml˜1 ng/ml.