Abstract: Despite the advantage of high average power output, a wide bandwidth ultrasonic transducer is needed in the ultrasonic ranging system with traditional continuous wave frequency modulation. But the transducer with wide bandwidth is not commonly available. This paper proposed a new method of distance measurement named the continuous wave narrow bandwidth frequency modulation (CWNBFM) method. An important feature of the ultrasonic ranging system with CWNBFM is that by using narrow bandwidth frequency modulation, a commonly commercial available ultrasonic transducer instead of the wide bandwidth ultrasonic transducer can be used in this system.