The invention relates to an ultrasonic 
transducer for flow detection, in particular to a transmitting-receiving 
underwater transducer which comprises a PPS (polyphenylene 
sulfite) housing, a piezoelectric 
chip, a backing layer and a matching 
adhesive glue, wherein a clamping spring, the backing layer and the piezoelectric 
chip are arranged in the space of the PPS housing from the inside out; the clamping spring is embedded into a clamping groove of the housing; the backing layer is made of sound absorbing rubber; and the piezoelectric 
chip and the housing are connected together through the matching 
adhesive glue mixed with a high-impedance material. Compared with the prior art, the piezoelectric chip and the backing layer are fixed and pressed tightly through the clamping spring so as to achieve a good sound absorbing effect of the backing layer and solve the problems that the output 
signal is unstable and the backing layer is not firm in bonding and easy to disengage due to the interference of the back reflection 
signal; and moreover, the piezoelectric chip and the PPS housing are connected together through the matching 
adhesive glue so as to realize the two-stage 
acoustic impedance matching of the chip and the liquid, and both the 
signal conversion ability and output signal stability are effectively improved.