The invention discloses a full-automatic detection method of liquid transparency. The method comprises the steps that a judgment criterion of a critical image or critical light intensity during determination of a transparency meter is established, wherein the transparency meter comprises an identification piece (2) placed into to-be-measured liquid and a camera (3) used for acquiring an image of the identification piece (2) or a photosensitive element; the critical image comes from the camera (3); the critical light intensity is detected by the photosensitive element; relative motion of the identification piece (2) and a detection liquid level of the to-be-measured liquid is realized until the critical image or the critical light intensity is captured; a distance from the identification piece (2) to the detection liquid level of the to-be-measured liquid is determined to obtain a transparency value. The method is used for solving the problems that an eyesight difference of determination personnel influences a determination result, an external light irradiation difference influences determination, a measured transparency value of a water body cannot be precisely expressed, the manual detection efficiency is lower and all-weather continuous determination is not facilitated.