Provided is a method for bottom touch recognition through an automatic water-gas medium recognizing bottom touch sensor. The sensor comprises a front cabin and a rear cabin. A gap is formed between the front cabin and the rear cabin. A transmitting ultrasonic wafer and a receiving ultrasonic wafer are installed in the front cabin and the rear cabin respectively. The two wafers are located on the two sides of the gap respectively. The cabins are further internally provided with a magnetic proximity switch and a detecting circuit, wherein the detecting circuit is composed of a micro power consumption single-chip microcomputer, an ultrasonic detecting module and a bottom touch detecting module. The method includes the steps of installing the sensor on a hoisting mechanism of a bottom sittingtype device, detecting whether bottom sitting happens or not according to the changes of the distance between a magnetic part and the magnetic proximity switch, and detecting whether the sensor enterswater or not according to the attenuation difference of ultrasonic waves in air and water. By means of the ultrasonic detection and magnetic switch combined method, the misoperation caused in the bottom touch process on a survey vessel deck is eliminated; by means of the micro power consumption single-chip microcomputer, the reliability and stability of output signals of the sensor are greatly improved; due to the four signal states of the sensor, the judgment applied in the operation process of oceanographic instruments can be expanded.