The invention relates to a water detection method, in particular to a method for detecting the water turbidity through an ultrasonic wave. An ultrasonic sensor A and an ultrasonic sensor B are adopted and symmetrically distributed at the two ends of the axis with the distance being L. The sensor A serves as a transmitter to send the ultrasonic wave to an opposite receiver B by the fixed excitation extension axis L, and the sensor B serves as a receiver to accept the ultrasonic wave sent by the sensor A; a voltage signal is converted through a signal conditioning circuit and an AD collection circuit, and the voltage signal amplitude received by the sensor B is measured. The turbidity can be calculated out through the relation of the calibrated turbidity and the voltage signal amplitude received by the sensor B. The method is simple in principle, high in precision, by means of a calibration method improving the turbidity and the received signal intensity, target measurement can be achieved, the amplification characteristic of a conditioning circuit is effectively improved, the measurement signal intensity is improved, and the high measurement precision is achieved.