The invention relates to a circuit for monitoring well kick at a deepwater drilling mud line. The circuit comprises an ultrasonic transceiving module connected with an ultrasonic sensor, and a measurement and control module which is connected with the transceiving module through an interface circuit and communicates with an upper host position, and is characterized in that: the ultrasonic transceiving module comprises a transceiving circuit, a passage switch and a power circuit; a microprocessor is arranged in the transceiving circuit, and generates an electric pulse driving signal with a certain frequency, a certain pulse width and a certain output power to excite the ultrasonic sensor; the measurement and control module comprises an amplifying circuit, a filtering circuit, an automatic gain control circuit, an analog-to-digital converter, a voltage conversion circuit and a digital signal processor which are connected with one another according to an input and output sequence; and the output end of the digital signal processor is connected with a digital-to-analog conversion circuit and a voltage regulation circuit sequentially. The circuit is arranged by the measurement of a Doppler effect, and can measure flows of a seabed marine riser and an annular drilling column in real time so as to immediately determine underground overflow situations.