The invention discloses a transurethral bladder ultrasonic detection method, a diagnostic apparatus and a transducer. The method comprises the steps that the ultrasonic transducer in the bladder is sent to the part to be detected of the bladder through an ultrasound catheter by passing through a urethra, wherein the center frequency of the ultrasonic transducer ranges from 5 MHz to 20 MHz, and the diameter of the ultrasound catheter ranges from 0.5 mm to 5 mm; ultrasonic signal are transmitted and received on the part to be detected of the bladder by 360 degrees; meanwhile, the the ultrasonic transducer in the bladder is withdrawn. The diagnostic apparatus comprises the ultrasound catheter of which the diameter ranges from 0.5 mm to 5 mm, the ultrasonic transducer, of which the center frequency ranges from 5 MHz to 20 MHz, in the bladder is installed at the front end of the ultrasound catheter, and the rear end of the ultrasound catheter is connected with a withdrawing and driving device; the withdrawing and driving device is connected with an electronic imaging system. The transducer comprises an ultrasonic transduction unit which is composed of a backing layer, a piezoelectric layer and an acoustic matching layer which are closely connected in sequence. According to the transurethral bladder ultrasonic detection method, the diagnostic apparatus and the transducer, the ultrasonic transducer is sent to the bladder part by passing through the urethra, the detection distance is shortened, the working frequency is increased, and therefore the imaging resolution is increased.