The invention provides a liquid clarity detection method, a liquid clarity detection system and a liquid clarity detection device. The method comprises the following steps: determining actual flow velocity of liquid, and determining measured flow velocity of the liquid by using an optical flow sensor; and determining liquid clarity according to the difference between the actual flow velocity and the measured flow velocity. A principle is as follows: the optical flow sensor acquires instantaneous displacement of a target according to the position change of an imaged bright point; when the liquid is in a dirty state, the imaged bright point is clear to facilitate the calculation of the liquid velocity, and the dirtier the liquid is, the more accurate the calculation of the liquid flow velocity is; and when the liquid is in a clear state, the imaged bright point is not obvious to be bad for calculation of the liquid speed, so the clearer the liquid is, the more the liquid flow velocity determined by the optical flow sensor tends to be zero. Therefore, the clarity of the liquid can be determined through a difference value between the liquid flow velocity determined by the optical flow sensor and the actual flow velocity of the liquid.